I feel this is just the natural trajectory for any VC-funded "service" that isn't actually profitable at the time you adopt it. Of course it's going to change for the worse to become profitable.
> It's owned by Microsoft.
I see no contradictions here.
And then many UI changes people have been complaining about are related to things like copilot being forcibly integrated - which is very much in the "Microsoft expect to gain a profit by encouraging it's use" camp.
It's pretty rare companies make a UI because they want a bad UI, it's normally a second order thing from other priorities - such as promoting other services or encouraging more ad impressions or similar.
If you have a captive audience, you can get away with making the product shittier because it's so difficult for anyone to move away from it - both from an engineering standpoint and from network effects.