I think that's just their SOP. When I tried to get disability for my bipolar years ago, they made me be evaluated by THEIR doctors. Guess they want to be sure nobody can slip through, fooling or cheating or manipulating "civilian" doctors. And of course I got turned down. Which is how I ended up more or less homeless for about 17 years, and a lot of other people do, too. Nobody chooses to be homeless, jobless and destitute, in spite of what you may have heard. The services that are supposed to be available to help people in need are often run by cynical people with no compassion whatsoever.