Originally Posted by paul21

It's not so much logic as it is legal restrictions. The federal government has some authority to restrict movements internationally, but interstate movement is mostly protected. It'd be up to individual airlines to impose a pre departure test to board, and then there's IDB rules etc., otherwise individual states can only impose a limited quarantine on arrival.

You're stating this as if some central medical authority decided it was best to test international arrivals and not domestic flights and therefore is a hypocrite or nonsensical. In practice this authority may have wanted both but could only secure one.