I had a friend who used to work for Simply Computers, back in the day (in the Watford office, I believe, but I may be wrong).
Then they were bought up / renamed by Misco.
Then Systemax bought up Misco.
Now Misco/Systemax look like they're dead. They also own WStore, and that uses the InMac name. These were all big names at some point in their existence.
I can't say I'm surprised. At one point, the days of flicking through PC Pro tomes as thick as your thumb looking at the shiny-new, they were some of the biggest... but even then I only used them for little commodity items. Neither I nor the guy who worked for them had a computer from them, even with the staff discount, and rarely used them for anything else.
Then mail-order became old-hat and, honestly, it took them a long time to work out what to sell. For the last 5-10 years they've been just a parts-pusher - in one door, out the other as quickly as feasibly possible. Standard stock. No unique selling point. The Maplin of the mail-order world - nothing they have that you couldn't get elsewhere cheaper, faster and more pleasantly but people used them because they'd always used them.
In all that time, I literally don't think I've ever ordered anything from any of those companies. They just couldn't come close to competing for business-level transactions, and they were too obscure for retail - people didn't know what they were buying, and those who knew went elsewhere. I can't think of a market they catered to. They used to phone me up occasionally or I'd use them as that handy "third-quote" because I know they'd be more expensive.
I'm sure they'll blame "Amazon" (or that CEO SEC filing controversy listed on their Wiki page) but those companies were in absolute freefall for many years and did nothing about it, besides making themselves even less relevant.
To be honest, nothing of value is being lost. They're box-pushers, and thinking that competes with others by standing out is a mistake. It's sad to see all the old names slowly being bought up, but that's because they just don't adapt.