I mean there's probably a political reason for it. It's "celebrity social media" proof that the virus really has little to no affect on healthy people. Also, where's your proof that lots of sick people are being denied tests? I walked into a hospital this week to dispute a bill and they were ready to test me on the spot. And I'm not even an old person (or at risk person).
I'm almost certain that hospitals at minimum put a priority on old and at risk people. Who cares if a young person has the cough and is denied a test (if they are even denied like you claim). They'll live.