Gonna talk from KDE positions here. GNOME, too, has its place, but I recognize it's not for everybody.

More pleasant to look at

Certainly not for the average person. For a normie user, KDE looks way way nicer, and it's certainly way more modern than either XFCE or Cinnamon. Sure, the latter can be made into something modernishly enough, but the customization options are way more limited here. Either way, out of the box, KDE is much more preferable to most.

User-friendly

Can hardly find anything that is more user-friendly than KDE. Everything you can possibly think of is available graphically, the interface is extremely sleek and ergonomic, and you can change anything at all to your liking. Which leads us to...

Customizable

Why would anyone say XFCE or Cinnamon are more cutomizable is beyond my comprehension. XFCE can be somewhat reasonably customized, but the anount of technical knowledge required to do anything more than resizing bars is beyond the scope of normal users. Cinnamon is outright rigid, and its customization options are extremely poor by any means. KDE is easily customizable and can be turned into anything through a what-you-see-is-what-you-get graphical editor that requires 0 technical knowledge. Still, if you really want to go the old school way because you're used to it, want something not offered, or can't imagine yourself descending into the GUI designed for plebs, you can do it too. KDE is king when it comes to this aspect.

Stable

As far as XFCE goes, this does hold quite some weight. It has a mature codebase, allowing it to have plenty of things figured out. For mission-critical systems, it might be preferable. Same can't be said for Cinnamon, but either way, every popular DE is stable enough for home use without much worry - including KDE.

In any case, having used all four, I stopped exactly at KDE and GNOME - the former being perfect for casual multitasking and entertainment, the latter being nice for focused work.

To each their own though? I can't imagine why anyone would want something other than i3 (or similar), because almost by definition the DE is not the program I fired up my computer to interact with, and i3 "gets out of the way better" than most others in my experience.

But...that's just my use case. It's a horrible UX for most people, just happens to work well for me.

My preferred DE is XFCE. However, over the past few months, I have moved most of my work to a new distro and made the jump to Wayland. Both of these have landed me on KDE.

KDE has by far the most complete, and therefore painless, Wayland support.

KDE has been great to use honestly. I mostly do not think about it which is what I want in a DE these days. The configurations I need are there when I need them and not in the way when I don’t. KDE uses more memory than XFCE but not nearly as much as Firefox or Chrome.

I dislike modern GNOME but KDE has been great and, at this point, I feel like it is the best option on Wayland.

Gnome devs have a clear vision of what Gnome is supposed to be: simplistic, designed for touchpad and keyboard, not mousy-clicky, and staying out of your way.

Nobody questioned this.

People install it, miss stuff they are used to from traditional desktops like Windows or Plasma, and bolt that back on using extensions from third parties.

Like the Extension feature intends it.

They install those extensions from a different source than Gnome itself (Gnome from their distro repos, extensions from the website).

Even those you can install from some distro repos can cause your whole Gnome DE to crash. However this isn't even the main problem; the point is that it's able to crash your DE at all. If they did it correctly only the bad extension would crash. If that doesn't work for some reason, the whole extension layer/API may crashes without taking the DE with it. If something phenomenally bad happens your DE should crash but, as the absolute minimum, your open applications should still keep working so you can save things and restart things gracefully. What you just did is blame the extension devs again.

And then they complain when those third party add-ons from a different source aren’t perfectly integrated or in sync after an update.

It's about your computer (well, everything graphically) crashing, not some small problems. Get your facts straight.

I don't blame GNOME devs, I blame the straight up lies from GNOME enthusiasts that GNOME is customizable, because it is not.

Conclusion: the clear vision that Gnome devs have is obviously wrong.

GNOME 2 was different and easy to customize

GNOME is still in their KDE 4.x days where it needs time to mature.

KDE 3 was loved, KDE 4 made a ton of breaking changes, and was reviled. KDE 5/6 are now butter smooth and fixed all the issues from the 3 -> 4 transition

GNOME 4/5 will probably come back into the loved category if they start stabilizing the extension system some more