I think it has more to do with the authors and their principles, and less with the times. There are plenty of counterexamples from that era: all major browsers, the Sonique audio player (which I loved for the UI novelty), Winamp itself, etc.
> any other software that has always worked and remained pretty much the same?
mpv is in that league for me, and it's much more recent. Then, of course, there are very stable CLI and power user software that has existed for decades: Vim, Emacs, BSD and Linux coreutils, etc. Some of these are not necessarily simple under the hood, but I use them because they do one thing well (or in the case of Vim/Emacs as much as I want them to do :)), and I know that they're not going to disappear or drastically change as so many software does.
IIRC, they were in a sort of PHP-looking scripting language? I had very little coding experience before then, so it was kind of a trip trying to debug why the lyrics panel would freak out under certain scenarios :D
I'm still using it to this day, with little more than an album tree, a playlist window, and an album art thumbnail that optionally all fold away.
I've been down the configuration | plugin trail, good fun for those of us that enjoy that kind of thing but it is | was simple and clean from a fresh install.
https://www.donationcoder.com/forum/index.php?topic=25334.0
Which does confirm that Faststone is faster but much water has passed under the bridge since 2011.
Irfanview is another “goes on every desktop install”. I even use it on Linux via wine.