The reason is Office
The reason because no one uses Linux on desktop is Office. The lack of, I mean. I use Linux since 25 years, and I'm fine with Libreoffice. I'm a sysadmin, so apart from Office, everything else is actually much better on Linux than on Windows, so for me it's easy. But for every other worker that uses a computer, it's simply impossible because there is no Office, no Autocad, no commercial program that they have to use.
And there is no solution to this because of course MS will never produce a Linux version of Office, the one and only program that allows them to rule the world. And no other commercial software will ever be ported to Linux until it has 50% of the desktop market, which it will never have because of there is no commercial software for a Linux desktop.
Now, SAAS has made a very tiny dent in this situation, since some (but not all) SAAS products work fine on a browser (I mean, on Chrome, only Chrome, always Chrome, no other browser than Chrome, it seems) on Linux. Not all of them becauuuuse.. OFFICE. Yes, they need Excel to work.
How can anyone win against windows and office in the current situation?