Because anticoagulants aren't the only things that can affect coagulation. If your PT is out of whack, something is wrong and they need to find out what that something is because it's not the NOAC, but giving a NOAC to someone with a prolonged PT might make them more susceptible to bleeds.
It's a cheap, easy test that they'd be foolish not to do on anyone taking any sort of anticoagulant or who's susceptible to clotting or bleeding.