I don't think it is nostalgia, I'd say that Windows 2000 was the peak when it comes to usability, and XP, Vista and 7 made it prettier, taking advantage of improved graphics hardware. And then Windows 8 arrived and broke everything.
It is easy to find the culprit: tablets, and mobile devices in general, and to a lesser extent, web apps.
Mobile devices needed a new kind of UI, something suitable for small touch screens. People tried things, apparently they are still trying, because it is a mess.
But now, we have another problem. Desktop UIs and Mobile UIs are very different. And this, in itself, is a bad thing. Mobile and desktop computers do a lot of the same thing, you shouldn't have to learn how to do it twice. So they tried to unify, and in the process, lost decades of UI refinement.
The next issue is portability. We have web apps, Desktop UIs, Mobile UIs, different OSes, etc... Developers don't want to make a different UI for every system, and users want consistency. The least common denominator is the web browser, so designers use that, but the web is made for documents, it is terrible for apps, but clever devs make do.
So as you see, we now have a lot of hard problems to solve at the same time, and the desktop UI became part of it.
> The flat "Metro" UI style was initially modeled and developed on Windows Phone 7,
Originally it was for Zune, which inspired Windows Phone 7, and then it was horrifically mangled for Windows 8.
WP7 Metro had a ton of affordances to make the phone easy to use, things like scrollable pages of content should always show a peek of content that is below the current view, so users know there is more content down below.
and it had its merits (from a phone-centric view) but the (crappy) UI remained even when there was not any more need for it (and a Windows 2000/Windows 7 like one would be much more suitable to laptos/desktops or anyway for no-touch devices).
It is easy to find the culprit: tablets, and mobile devices in general, and to a lesser extent, web apps.
Mobile devices needed a new kind of UI, something suitable for small touch screens. People tried things, apparently they are still trying, because it is a mess.
But now, we have another problem. Desktop UIs and Mobile UIs are very different. And this, in itself, is a bad thing. Mobile and desktop computers do a lot of the same thing, you shouldn't have to learn how to do it twice. So they tried to unify, and in the process, lost decades of UI refinement.
The next issue is portability. We have web apps, Desktop UIs, Mobile UIs, different OSes, etc... Developers don't want to make a different UI for every system, and users want consistency. The least common denominator is the web browser, so designers use that, but the web is made for documents, it is terrible for apps, but clever devs make do.
So as you see, we now have a lot of hard problems to solve at the same time, and the desktop UI became part of it.