Re: "were made available for other OS"
Mate, Cinnamon, Gnome, KDE, and even vtwm have multiple desktops and have had them since 2005 or earlier.
But, Bob - that's half the problem. You've banged out 5 different window managers right there. Your average user doesn't want five different window managers. They just want one. One that works. One that works sort-of like their old one. One that they know their way around, and that they can collar their nephew into talking them through a fix over the phone.
I've said before about toothpaste. Too many choices! Windows, you get one UI and everybody is (in the main) happy. If they don't like it they can buy a Mac where you get one (slightly different) UI. If you don't like that, sure there's Linux, but people stumble over "do I want Kubuntu, Lubuntu, Xubuntu, What-the-fuckbuntu?"
Choice is sometimes overrated.
Also, I'll take this opportunity to apologise for being rude the other day. Too little sleep and not really any good excuse. You're a bit rabid, and your Linux flag-waving is a bit too much like zealotry for the real world that I live in, but the place would be missing something without your foil-hatted rants!