From a marketing perspective perhaps, but it's still a supported LTS release of Ubuntu at heart and having two different version numbers would create ambiguity.

Things that should work on that particular Ubuntu LTS should work in Pop_OS! And at least you don't have to cross reference things.

Thankfully they keep important things more up to date with newer kernels/hardware support than the version numbers would suggest, but I think that it's a common point of confusion.