If your computer is compromised to the extent that bad guys can read memory allocated to your password manager in order to discover the key to your password database, then they can also read memory allocated to your browser, which temporarily stores your passwords when you type them into websites, and steal the passwords from there.

Even storing passwords in unencrypted text files only reveals them to bad guys if they have compromised your computer to the extent that they can read arbitrary files, in which case the bad guys can also read all the other sensitive information stored on your computer. Depending on what you do for a living, your porn preferences, etc, that may be even worse than your passwords being stolen.

And that sort of security breach isn’t terribly common anyway. As long as you don’t run any shady software on your computer, it will most likely never happen. Using weak passwords, on the other hand, will result in the compromise of whatever they protect, because cybercriminals are constantly, relentlessly trying to guess people’s passwords.