I feel like the downvote button in special should / could be multidimensional. People downvote content out of multiple reasons: "this is incorrect", "this is really dumb", "this is off-topic", "the poster is a jerk", so goes on.
IMO this would combo really well with the experimental study in the OP.
They saw Lemmy becoming successful, corporate mistook Lemmy with Lemmings, and decided to go out Lemmings style.
...jokes aside, Cory Doctorow has a great text about that, called "Tiktok's enshittification". It's a four-steps process:
In my opinion it's also the result of management being disconnected from the platform that it manages, and not knowing fully the implications of their own decisions.
I'm not a big fan of fishing mechanics, they're usually shallow "press button at random signal, get a random prize" mechanics.
Also escort missions where the NPC being escorted does not understand that it should protect its own life. I don't mind repeating a mission due to my own mistakes, but I don't want to do it because some AI went potato.