Mike can edit his name and his bio. He could edit some karma metric that he's got view access to but no write access to. That's fine, I can introduce an RLS policy to control this. Now Mike wants to edit his e-mail.
Now I need to send a confirmation e-mail to make sure the e-mail is valid, but at this point I can't protect the integrity of the database with RLS because the e-mail/receipt/confirm loop lives outside the database entirely. I can attach webhooks for this and use pg_net, but I could quickly have a lot of triggers firing webhooks inside my database and now most of my business logic is trapped in SQL and is at the mercy of how far pg_net will scale the increasing amount of triggers on a growing database.
Even for simple CRUD apps, there's so much else happening outside of the database that makes this get really gnarly really fast.