> It's pretty obvious that they think the distinction is worth having because they can vet apps they signed

This is an assumption made in exceptionally generous good faith. It's certainly possible, but I would argue this is far from obvious, & there's enough circumstantial evidence to support this being completely untrue.

Sure, Google can vet apps they sign. Whether having this ability is their primary motivation for having a distinction (or whether they will actually vet apps they sign) is a very different question.