[weikju]

Because the attestations will only work on iOS and Google Play integrity attested devices. Meaning Apple and Google accounts required.

[blitzar]

A phone is also required then?

[livvy]

This is an assumption, but not confirmed.

[AppAttestationz]

I spent months designing a system, exactly like this. An account is not needed, at least for Apple.

Play Integrity could the worst offender here, as it can be leveraged to force a user to have installed the app through the Play Store. Indirectly, requiring a Google account.