I don’t think it’s been clearly voiced enough, but there are thousands of sub moderation bots that do things like automatically flag hate speech for mod review that will all just stop working. Some of the larger, older subs have entire ecosystems of content tagging and linking that will break. An example is putting the name of a tv show in braces [TNGS01E13] and getting a link to that episode’s wiki as a comment reply. It dramatically improves the Reddit experience, but isn’t worth the outrageous cost to keep going.
Overnight, Reddit would turn into a (more) poorly moderated nightmare.