[__MatrixMan__]

There's a bit of a gold rush on to be in control of all of a user's auth, and TPMs are a precondition to maintaining that control.

The passkey protocol (i.e. webauthn) has an "attestation object" field which organizations like Microsoft can use to pass extra details about the authenticated users to the authenticating service. Which details will likely depend on that service's relationship with Microsoft. Unlike most channels between these parties, it's expected to be secured via TPM thereby excluding others (e.g. the user, or any pesky researchers) from the conversation.

It's pretty obvious from the recent design choices re: Windows that Microsoft is keen on monetizing user data--and who, in that business, wouldn't like a way to do it exclusively? i.e. to control a channel which neither the user nor your competitors can tamper with.

So they'd be incentivized to make you buy new hardware because new hardware allows them to bind your advertiser id to actual identity much more closely than is possible without that hardware (e.g. via cookies and IP addresses). The sale of details about your actual identity to organizations who only know you by your advertiser id is big business. The TPM helps them protect that business against competitors who don't have such low-level control over your device (Google, Meta, etc).