Sunk cost fallacy is probably the most obvious one that springs to mind. Not unlike gambling in a sense, people feel they just need one big payout to win it all back and then some, so they keep betting, hoping that this time things will go in their favour.

It used to in the past. It was removed in the 0.19.0 release. This is the pull request that took it out (I think).

This thread has some of the reasoning for it, but at a high level the Lemmy devs made a call that the benefits a karma system provide didn’t outweigh the problems a karma system can cause.