The main argument to use password managers to prevent password leaks to all of your services (that you use with the same login/email). You can't trust any service to store your password securely, therefore you should use different ones everywhere.

Using a password manager gives you the convenience of using one, strong password that's being used very securely, and mitigating risk of password leaks spreading further.

If you abstract it that way, it by no means eliminates the risk of someone breaking into your database, but makes it harder and from a single entry point, instead of any service that uses your password.

Plus many of those password managers give you an option to use YubiKey for additional security.

Oh and also you won't ever need to press "forgot password" ever again due to the arbitrary requirements that your password doesn't pass, so you modify it slightly so it would.