A database has to handle situations outside its control, e.g. someone cutting the power to the server. That should not result in a corrupted database, and with Postgres it doesn't.

The fundamental problem is that when you're sharing memory, you cannot safely just stop a single process when encountering an unexpected error. You do not know the current state of your shared data, and if it could lead to further corruption. So restarting everything is the only safe choice in this case.