I work in a private mental health (social workers and psychologists) practice. Here is what I know about Medicare.

Most often PT services must be prescribed by a physician.

Then the physical therapist (or in our case mental health provider) must have the required credentials for Medicare to approve payment for services. In our practice we are all Medicare-approved (licensed Ph.D. in psychology, MSW in social work). That is the first step. This first approval process can take one or more months. Then, the billing process is far more complicated than billing through private insurance such as BCBS or Aetna. The reimbursement that we finally receive is about 30% less than what we collect from private insurance.

I suspect that some of the PTs that you've encountered do not take Medicare for the reasons I stated above. In addition, a PTA (PT assistant) cannot qualify for Medicare unless they work under the direction of a fully qualified provider such as a PT.

Confused? Yes, it's a perplexing process but this is how it works across the U.S.