I'll assume for half a moment that the question in the subject title is an honest one and take a stab at answering it (without making any value judgments in the process, lol):
Because anyone who wants to develop applications, DEs, et cetera for linux can - and does - do so and there is no requirement that those things operate in the same way. In this one small (no, not really
) regard, I'll give the Microsoft Windows world the nod for at least the appearance
of having a set of standards(?) in how things operate. For example, most every app I ever used (IIRC - it has been "a while") in a Microsoft OS allowed the user to quit it by pressing Alt-f and then q. And even if that didn't work, Alt-F4 did. With linux, well... flip a coin as to whether or not the method of quitting an app that you used on the one you just quit will work on the next app you run....
I always figured that was why some people have been known to say that using linux could, at times, be akin to herding 100 angry cats. That were schizophrenic. And on acid. Enjoyable, sure, lol, but occasionally a bit interesting
. Still, it's sort of like democracy: It's not the best - but it is the best that humans have come up with to date. I like it (linux, I mean).