Inside Microsoft they must have workshopped this. I'm going with "it's good for everyone in the supply chain" thinking.
I also believe tpm and related trust hardware aside, it was a decision which could have gone the other direction.
But that trust issue, is now cross (commercial) industry. OSX and iOS and android all now depend on hardware trust chipsets which aren't in older technology, I would think W11 might run without but not officially. The version of secure execution has a version dependency. TPM 2.0 nothing earlier.
Virtual TPM make this all a bit meta. Maybe older kit exists which can't run W11 native but can under a hypervisor? It might be hypervisor capable chipsets wind up having suitable TPM support anyway.