things that are a bit silly but competitive players like
This is the honestly the best summary of almost any question like this imo.
Fighting games in general have a spike of general interest, and then settle down to be kept alive by the more hardcore. And once that more hardcore group adjusted to a version they were particularly reluctant to re-learn a new one. (This has changed in modern patch culture, but people have no real choice anymore. Plenty of bellyaching about it though!)
It's similar to how people don't play the revision of 3rd Strike.
Perfect example. Unblockables are, on the face of it, a game breaking bug you'd think people would want out. They also are what makes Urien a competitive character, without them he's just not good enough. But this only really applies at a high enough level to learn aegis setups. It's the hardcore driving this kind of decision because the casual players just don't exist in any real numbers to have a say.
Zero 3 Upper is also a bit weird for a few extra reasons:
1) It came out quite a while after the original, which really exacerbated the established player base vs change problem, people had been playing a certain way for years at that point, why re-learn characters and strategy? Ask Arturo what he thinks about Sim getting nerfed lol.
2) As a Naomi release instead of CPS2 it was going to feel different in various ways. I don't know if the input lag is worse or not, be interesting to test that, but it's going to look different since it's probably running on 31khz monitors for instance. It wasn't a true drop in replacement for the old game.
3) There's only Zero 3 Upper, no Alpha 3 Upper, the West never got it at all. I know players who think of it as a "console" game because of that, it wasn't ever seen as an arcade release in the US or taken seriously because of that. (Again, sign of the times, in that era arcade still ruled and console was seen as inferior, now games barely get arcade releases and almost no one cares.)
I personally find crouch cancel infinites deathly boring to watch. It's too bad it never took off, I'd be curious to see a competitive scene that was serious about it. But the difficulty of running it, both in a tournament setting and at home for players to practice, really hurts that too, even looking past the arcade era problems.