~ how is that different than having 50 different accounts all using the same password?

Because the password manager would have to be hacked itself.

If you just use the same password for everything, any of those 50 sites could be hacked.

1. A password managed is basically like a physical vault. If someone gets into a physical vault, they’ve gained access to all your valuable items, but the vault is extremely difficult to get into.
2. Random websites do not prioritize security like they should. So when there is inevitably a breach in one of those 50 sites and you end up on haveibeenpwned.com, that does not allow them access to the other 49 sites. Often when logins are breached, the people getting that information do not care about the actual site that was breached. Rather, they know a password you use and your email, and can now try to login to actually useful sites where people often use the same login.
3. There should be multiple layers of security to your password manager. Password and Authenticator app should be basic (No SMS or Email 2FA, not secure enough). Ideally, we move towards passwordless logins altogether so there is no secret that can be compromised on the server side.

1. With a long enough passphrase, your keepass db is uncrackable by any current tech.
2. If you have 50 accounts using the same password, if any one of those websites get hacked, they now have access to every other account.

I like your thinking. Here an example why password manager make sense. If you would use the same password at every website and one of the would be for example Facebook, and they would get breached. Your password associated with your username and email , is now know to some hacker group. And in case of Facebook, the password is not hashed , it was stored in plain text. Now they have fun to try different websites with combinations of your name , email and password.

Alternatively a password manager stores for every website a different password, and your only mission is to keep that manager secure with a good , rememberable password.

Also , what I do , is using an email alias service. So I have a different Password and Email for each account. I don’t have to care if something gets breached, I am safe and aware of what information gets stolen.

And for future, we could all use passkeys and FIDO2 to block most phishing attempts.

If you use an easy password for your password manager, it’s trivial to crack with a few word lists and hashcat, just as any other account.

Websites get hacked all the time, and your login details (and PII) ARE available for sale from shady people right now. It’s important that, the next time one of the sites you use gets hacked, you don’t have to scramble to update all your other logins.

If you don’t use a second factor to unlock your password database then you are correct.

Here is the real secret. If the only authentication you have on an account is password auth then you really have no authentication at all. Passwords are not security