Mods used third party tools to help them with their unpaid work. These tools relied on access to the reddit api.

Then reddit charged ridiculous prices for api access, which would mean the apps would need money, so mods would need to pay to do their unpaid work or use the inferior reddit interface.

Given these choices, some mods decided to leave instead.

A short name for communities would be groups. I like to call the users fedizens, as it is not specific to one software.

Yes, using Emacs is more important than the OS.