Would you care to elaborate? It also matters what counts as "bad password manager" to you - Poor crypto? Poor UX? A reddit post ;-)? LastPass?
With passkeys, both the website and the user can be pretty sure that the "password" is secure. The website knows that it's based on enough entropy, and the user knows that the website can not loose it.
Of course if I use a random generated 80 char password I only mildly care if the website stores it plain text or not.
But if I was a site operator, I could additionally trust that the users are using secure passwords. Without insane strength requirements (which people only work around anyway, e.g. Passw0rd!123 is usually accepted, but thisisasuperlongpassphrase often is not).
I'm in the business of testing security, which means I sometimes crack passwords. No matter how much training you put your employees through: Somebody gonna use ${some name}${0 or 1 special char}${some birthday} - is it's the spouse, kids or affairs data, your guess is as good as mine.