Are you using every single one of the 100+ accounts constantly? No? Then you can do the passkey flow on demand as needed. It can be comparably simple as an email login or 'we emailed you an OTP' login confirmation flow. If you never get around to using the account ever again in your life, I suppose you never needed it?

If the website is momentarily down how are you going to access it with a password at that moment? You'd have to wait until it came back up. And then you could just as well set up the passkey.