Users hate them.
The typical user has dozens of username-password combinations. Managing them is cumbersome, time-consuming, and complicated.
Hackers love them.
Websites store passwords with user account information. A breach of one website can give the hacker access to other sites for the same user.
They’re not secure.
It is virtually impossible to keep a secret on the Internet. Passwords are a shared secret, and password databases are routinely breached by hackers.