I've seen docs do chest compressions 3 or 4 times. At night on many floors, there aren't that many people around and often times untill the code team arrives there may be only be a few nurses around - any doc that happens to be on the floor is grabbed and made to get to work. With multiple codes on the same floor or even in the same hosptial, docs are fair game to recurit for CPR. These days we have a big nurse shortage and new nurses will sometimes defer to doc.
BTW: Did you even read the article that this whole thread is based on? It's based on nurses AND DOCTORS doing CPR
And, of course, there aren't many medics in the hosptial.
And, btw, yes - a nurse runs the code.