Memorizing passwords doesn’t scale well.

You’ve likely got dozens of accounts. You’re not going to memorize a password for every account. Re-using passwords is a serious security problem though. Poorly secured sites get their password databases leaked all the time. If you use the same password on lots of sites, it’s basically a sure thing that the hashes are out there on the darkweb already along with your email, and your password is compromised.

Also, typing your email password into an unsecured library computer is a terrible idea. It is ridiculously easy for someone to install a keylogger and gather emails and passwords. In the past, your main protection was that it wasn’t worth anyone’s time to break into the computers, install keyloggers, collect lists of passwords, then figure out how to use them to get money. But with LLMs that can all be automated. It has become ridiculously cheap, and can be done by someone with a bot farm in Russia.

A password manager largely fixes the first problem, but at that point you need a device with your password manager with you to log in anyway. And the password manager doesn’t fix the second problem at all.