I mean... There are a zillion reasons this isn't trivial. Imagine I have an app that pays you, and it has to report taxes on it. It can't just delete your info. Imagine an app that sells alcohol, maybe it needs to make sure it has confirmation of your age/info in case of legal action. Imagine a chat application, if you chatted with someone and they deleted their account, would you lose the chat information (or even the name/record of who you chatted with?), no, that's 'your' information too, somehow.