Yeah, lemmy using the ! for communities kinda screws it up across the board. Some apps can't seem to make it be recognized as a community tag, and it makes the spoiler markdown annoying as hell.
I really wish they'd picked a less important marker for communities. ¢ is like, never used for anything and kinda looks like the c/ thing in a way lol.
No clue. But it seems to be most common among people that are most likely to believe that they should be able to say whatever they want, wherever and whenever they want.