XP also had the benefit of riding Moore's law for so long that the "high hardware requirements" became lower than the cheapest hardware you could buy halfway through its useful lifetime, which helps with its perception.
That all went away as SSDs came on the market, but it was a noticeable "downgrade" from teh snappy.
The Ghost of Bushes Past continue to haunt us, I suppose.
I think Gnome 3 is the most successful, because their utilities and first party apps have the right kind of compromise while not trying to enforce their view on other software workflow. iPad OS would have been great too, if they went for a free floating windows management and some widget redesign instead of the awkward stage manager.
I'm not gonna gainsay anyone who says it was good, I'm sure they have lots of legitimate fond memories of Space Cadet Pinball, Half-Life 2, etc. But the Windows XP era was the first one where "what's happening with Windows" just passed me by. I was through with Microsoft's shenanigans starting around then.
For those in the know, that was great. Windows XP + classic theme + drivers (even if you had to find the W2k drivers) was incredibly stable and performant.
But it took a few years for games to catch up and get the updates, and so for the "tech oriented" crowd (which were often gamers), it took a bit to catch on.
But its longevity is a tribute to how "good it was" and how hard it was to improve from it. Vista introduced more stability at the expense of requiring new drivers, so they re-released Vista a few years later as 7 (there's really no major differences between Vista and 7 except a few years of upgrades to drivers and hardware).
The five years between XP and Vista certainly didn't help matters, either. If you wait that long, you better be willing to support it for decades. Windows XP's last update was 18 years after it was shipped.