Why WebAuthn (passkeys' underlying technology) doesn't take off as expected. The main arguments in the comments:
Many edge cases and novelty for devs:
There's so many ways use this tech and so many cases and flows that you have
to consider
New login pattern: many users haven't used their biometric unlock for web services yet and need to be educated
Cross-device & cross-platform questions: different UX on different browsers and devices need to be considered
Lack of support by auth providers and tech stack: many existing authentication providers have no easy option to
enable passkeys for most prevalent tech stacks