You’re looking at this from the perspective of an educated end user. You’re pretty secure already from some common attack vectors. You’re also in the minority. Passkeys are largely about the health of the entire ecosystem. Not only do they protect against credentials being stolen, they also protect against phishing attacks because identity verification is built in. That is of huge value if you’re administering a site. Yes if everyone used a password manager there would be less value, but only about a third of users do that. And as an admin you can’t just say “well that guy got phished but it’s his own fault for not using a password manager.”
Password managers have only really taken off in the last half-decade, so one-third is kind of to be expected. I know they’ve been around a long time, but major adoption has been recent.
Passkeys will take a while to get wide adoption as well, especially with syncing problems that we’ve seen.
Password managers are never going to hit anywhere near 100% adoption rate. It requires knowledge on the part of the user and in many cases money. No grandma isn’t going to roll her own with keepass. Most likely she’ll never even know what a password manager is. And as long as those users are still out there, admins still have to deal with all the problems they bring.
Incidentally I looked and it’s been over a decade since I started using my first password manager. They’re not that new.