I'm going to guess it's part A/B engagement testing and part copying the whatever is hot (TikTok). The engagement tests only show what's currently "working" and doesn't correspond to long-term resentment, like what you're seeing in the comments here and everywhere else.

In the end though, I don't think it matters. The majority of users will stay. Switching platforms means losing your friends, your familiarity, and your time.

the answer is really simple. monkey see, monkey do.

the question was intended to spark introspection

the simple answer is that people copy. there are too many infinite permutations to incentivize reinventing the wheel.

a newer example being how ChatGPT simply showed people what product market fit is, various people and organizations had similar AI products and just didn't know that's what would hit. Google was sitting on one for years earlier its engineers were too busy getting finessed by it. Suddenly Google sees "oh, thats what we can do with it" and now Bard is out.

Its the same with UX patterns.