Re: Why Windows?
I'll answer from 20 years of IT Management experience.
Because most places that you ask for help cannot/won't touch Linux, hiring a person who "knows Linux" is far harder than one who "knows" Windows (definition of "knows" left as an exercise to the reader), and most tech support, IT, consultancy, etc. companies dealing with small businesses will run a mile from a Linux box and tell you to just replace it with a Windows equivalent.
People nowadays are scared of the command line, petrified of anything that doesn't have Windows Updates and run from anything that doesn't have a taskbar with the AV running in the corner. They'll use a Linux box if it just turns on and presents a website on an IP but otherwise they won't ever want to configure it.
Now that's a crass generalisation, but it's pretty true, in my experience.
Have a look at nComputing - they sell little terminal services boxes that just log into a server, like a mini Citrix, and display the screen / send mouse movements. Their boxes are running "something". They can connect to a server running either Windows with an expensive TS licence, or Linux. In fact the newer client boxes are literally nothing more than a RPi3 in a fancy box. And how are most sold systems configured? Windows servers.
I have an access control product. It's written in Java, perfectly well has support for both Linux and Windows and even Linux-specific instructions for install, etc. It spends its life doing backend work and presenting a web page to configure it from, then talking UDP out to the actual door control devices (which run on a form of Linux). The engineers are very friendly with me (a long-term customer) but still tell me they only ever configure it on Windows machines.
Same for everything. Hell, I see Windows running PBX boxes, which I find laughable. "Engineers" and "consultants" from all kinds of places come in and look at my systems and hate that I have some LAMP stacks running websites. They don't understand it. It hasn't got a GUI.
I called out a specialist IBM-certified engineer once for some emergency work on a BladeCenter (blade server chassis with integrated networking, storage, etc.). I needed them to access the iSCSI-offered storage so we could recover it. No matter how much I said it, they avoided everything they could to use the SSH-based tool that lets you do it in seconds (I know it does, and I know how to do it, because that's what I used to configure the whole thing, but this was a "you're the expert, you fix it" scenario for them so I was hands-off on it on the orders of my boss). When they couldn't get into the web-interface, they were stuffed, baffled, unable to continue. Hours and hours and hours of playing about trying to get the web interface to work and restarting the whole thing, for the sake of three SSH command lines. In the end, they literally bodged it by putting a blade in a previously-allocated slot and reading the storage from the blade (which had to boot up into Windows and be configured to pull in the iSCSI and so on). If that blade config hadn't been in place, or the storage in any way faulty, they would have been stuffed.
It's about maintainability. Everywhere I go, I'm allowed put in Linux because it's free and I'm managing it. As soon as I make noises to leave, and other people are brought in, the first thing they ever want to do is ditch/replace all the Linux-based things, even standardised devices running on support contracts (e.g. our visitor management is Linux on a support contract, our web filter the same, etc.). Those they see as ripe for replacement with their own solution, but Windows ones, they never do.
Their engineers universally don't understand, haven't tried, don't use, or have decades-old scare-stories of Linux that keep them away from it at all costs. I literally have some in my office as I speak. Outside company putting in a cloud backup solution. Windows agents, all just install. Linux agents - they're baffled when they don't work, have no recourse, have to go back to the backup providers, etc. etc. etc.
Linux is a second-class citizen in small business IT. Datacentres, sure. But mom-n-pop shops, IT guys who just want to come in and get Office working for you, engineers that setup digital signage, access control, CCTV, etc.? Unless the devices comes pre-loaded and just runs a website, and that can all be accessed and configured from Windows? Forget it.
Everywhere I've worked with techy-bosses, I've been able to deploy Linux and save a ton of money (on OS licensing, service costs, and things like TS licences, Exchange licences, web-filtering, etc.). Every time they leave, I leave or I go somewhere else... it all gets wiped back to pure-Windows and/or expensive off-the-shelf boxes that do less and cost more.
I've given up on trying to argue it, to be honest. I've met so few people in my career that have even used Linux in any fashion seriously (beyond "Yeah, I tried it 20 years ago but you had to create your own modelines in X so I never touched it again") that I realise the exact problem. The friends I have in the industry who know it inside out and use it themselves are all developers or in the higher-end of IT (e.g. Google datacentres, Rackspace, cloud providers, etc.). I am a complete outlier, trying to use Linux, which I'm extremely comfortable with, demonstrating its benefits, and yet having full control of the IT, and yet occasionally having to pass it off to someone else. Nobody's interested. They all just see it as an opportunity to sell you their Windows-based alternatives that are less powerful and more costly, or sell you an embedded Linux box where you can't get to the Linux parts at all but it "just works".
Honestly? The answer's simple. You want an engineer who did a day's course on the system 6 years ago to walk into a customer site and fix it within minutes. And it's easier and quicker to deploy it on Windows, and let their knowledge of Windows get them through downloading the installer, saving it on the desktop, running it, and then rebooting.
And most companies that write their own program or sell things like digital-signage don't care that it's Windows and licenced. The customers are paying that. But it's a lot easier to find a .NET dev than a Linux guy, a pre-loaded Windows machine than a version of Linux that installs from disc and just works on UEFI etc., and an engineer who just needs to remember where Control Panel is nowadays rather than teach them to use a Linux system.
And, I have to say, the only system I have that is solely Linux and sold as a Linux box and provided to customers, the visitor-management system, sucks. Some guy knocked something up in Python, lobbed it on a machine, and they supply you with a VHD of a Linux server and pre-loaded Ubuntu machines with the scripts on. It just runs X, runs Chrome, goes into full-screen and loads a local webpage. It falls over, it doesn't work with multiple monitors (e.g. to let a secretary see what the visitor is struggling with), it prompts with crash warnings from Chrome all the time (because it wasn't properly shut down - and they haven't bothered to change the Chrome options), and only one guy at the company understands it, so everything you ask has to be filtered through the busiest guy in the company and then passed third-hand back to you as a customer.
Linux is very much either a black-box, or a "geek son of the company director made a product and he's the only one who understands it".
And I'd like to point out - I ran Linux-only for 15 years, I supported a Linux distro called Freesco back in the floppy days (and my box for that ran my network for 15 years!), I put Linux into every workplace I work in (eventually, when it's been okayed with the above caveats), and I love Linux.
But everything sold with Linux anything more than a black-box sucks or is effectively unsupported.
Case in point: I took over a new job running the IT for a private school. They'd had their IT suite converted (terribly) to Linux. It sucked as a desktop environment for them. I scrapped it. With a heavy heart, but it just wasn't fit-for-purpose. It was cobbled together (by a professional company!) with cheap server, junky implementation, Cygwin-based tools and trying to coax Wine to do stuff. We scrapped it, after they asked if there was any hope for it. It took me five years to get Linux back onto a desktop in that school (server-side, very different obviously). And that was a bunch of new-at-the-time Netbooks... load up a cheap netbook without a Windows licence, slap Ubuntu on, configure the desktop, turn it into what we'd today call a Chromebook. They worked well enough.
When I moved on a year or so later (after my boss moved on), I know that all those netbooks ended up in the bin, and everything Linux was just ripped out and replace with boxes costing 2-3 times as much as the original purchase price. Because they couldn't find anyone to support them.
Irony: My next place, after many years, then demanded Chromebooks. Which are literally just Linux desktops running only Chrome. But they're supported and people know what they are, and you don't have to do anything fancy - they either work, or they're cheap enough to bin.
Windows machines own the market for no technical, ethical, cost or other reason. Than "the 23-year-old engineers grew up with them". That's it.