There's a very good talk by Moxie "the ecosystem is moving"[1][2] and the reason you need your software to be changing constantly, even when it's doing one thing well, is because all other software is changing, moving requirements, compatibility, and integrations.
Also, it's not like we have no progress in UX. I quite like the light/dark theme in apps changing according to the time of day. It only really started working well within the last two years after all apps adapted.
[1] https://signal.org/blog/the-ecosystem-is-moving/ [2] https://www.youtube.com/watch?v=Nj3YFprqAr8
> a product that serves a relatively simple and clear-cut need like a bookmark stash
By the same reductionist logic, you could argue that people don't need a bookmarking service at all, they can just save bookmarks in a text file. Simple, clear-cut. No fuss.