One thing I’ve never understood about “kernel never breaks user space”.. doesn’t that completely atrophy the kernel, preventing it from ever having big rewrites or architectural changes? What if an initial implantation was terrible, and there are 100x performance improvements to be had by doing a breaking change?

They didn't "give the keys", they have a signing infrastructure that is meant to be used for validating organizational identity and origins of code. They have a quality checking system, but it's only required for certain levels of Microsoft backing. I think it used to be called the Windows Logo Program or something?

Signing is meant only to verify the identity of the organization producing the signed artifact.

It’s not meant to signify that it’s bug-free.

The issue was caused by a data file, Microsoft is not involved in signing or testing individual data files.