We fake users inputing text to input boxes and spend crazy time figuring out how to do that and how to get around various sites trying to block that, so the site can still pretend it’s actual user inputting the password. Plus the manager needs to work around arbitrary password rules. Plus they usually don’t work at OS level; so you still need to remember that stupid iTunes password, that stupid Windows password, that stupid Google password on Android login. Plus you still need random PINs in random banks and other systems.
It’s better than memorizing, of course, and slightly better than writing it on paper somewhere (although that’s actually not that horrible honestly).
It’s just, they feel like a patch-fix from 1990s to a problem from 1990s.
I don’t want password manager. I wish I didn’t need password manager.