We had originally planned to go all-in on passkeys for ONCE/Campfire, and we built the early authentication system entirely around that. It was not a simple setup! Handling passkeys properly is surprisingly complicated on the backend, but we got it done. Unfortunately, the user experience kinda sucked, so we ended up ripping it all out...
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.