It's a combination of whimsical requirements from PMs and designers, plus FOMO and resume-driven development among developers. None of which have anything to do with actual end-user needs.

There's also a Large Corp dynamic, where to maintain consistent user experience across the product portfolio, a common UI platform is built. The platform is then mainly driven by the requirements of the most dynamically interactive applications, leading to a complexity creep - even though most of the products could be simple CRUD web pages.

"resume-driven development"

I think you nailed it.

And on top of that, most users want it to work the same it worked yesterday. Nothing drives me up the wall more than neverending stream of updates for anything and everything, be it PC, mobile, web, even cars. I understand it's great for job security and/or resume-filling, I just wish those developers would consider the difficulty of,for example, trying to explain to 60 years old nurse why the thing that worked yesterday doesn't work anymore or why it suddenly behaves differently.

Companies overhire devs after raising money so it looks like they're doing a lot of interesting stuff. PMs and managers need to find stuff for these devs to do, hence they come up with overcomplicating their existing tech, redesigns, etc.