This is connected with windows 11 requiring a TPM. If all their users have a Microsoft account and that Microsoft account is needed to access all their passkeys, then they end up with a privileged position where they can aggregate info about user behavior based on their logins which, thanks to the TPM, the user is cryptographically locked out of interfering with, and their competitors are locked out of participating in by the fact that Microsoft controls the client.

As always, it's about controlling users via high switching costs. I hope we come up with an improved webauthn spec which ruins this for them.