Data privacy laws like GDPR probably require them to fully hard delete when a user asks for something to be deleted. So any undo functionality would need to make sure it's compliant in every region that could have a privacy law. I'm not sure how realistic it would be to ask companies like Github to jump through all those hoops because people refused to read (and then blindly typed stuff out).
I'm pretty sure GDPR doesn't say everything must be wiped instantly but instead within a reasonable time period. One that's certainly enough to undo such actions.
