We’ve got different ideas about what’s not “that bad”.
Assuming that such things are “harmless fun” and can be done with no meanness involved is a large chunk of the problem.
I wouldn’t have come on the board in order to announce why I wasn’t joining the board. I don’t expect that everyone who did join the board, but then quit later on, announced their reasons for leaving.
Because I’m not seeing the extreme extent of such crap that some people are describing (I didn’t join these boards until 2019); and because when I do see such crap I see pushback.
Most of the threads I read don’t have anything overt, and when it does show up it very often gets modded.