I have a theory that corporations make new UIs to entertain people through them. First, to create the feeling that something is happening, and second, to increase screen time.
Old interfaces were far more practical for getting work done, and therefore obviously boring.
For me, as someone who is supposed to use technology as a tool and not as a source of amusement, the new interfaces of the major OSes feel unacceptable. But the other billion people chatting and scrolling are the real consumers, not me — and as a result, we now have the interfaces we have.
That’s one reason corporations make new UIs, yes, but the other is users demanding them for the sake of novelty. Reddit (but not only) is filled with people with no design sense complaining about how something which works (because it was relentlessly iterated on) looks “stale” and “old”. They’re the same users who jump from app to app willy nilly just chasing novelty. Any turd, if hyped enough, is ailed as “the future”, “modern”, “innovative”, which is repeated drivel from what the corporations tell you when they introduce their next thing.
Not really a theory.
Software makers treat UIs the way auto makers treat paint and body styling.