The cash prizes are inconsequential compared to the liability a physician would take on. There are exactly zero insurance carriers that would cover any malpractice claim as a result of consulting on this site. Despite what the FAQ says about this "not constituting a doctor patient relationship." Good luck with that in court.
Um, most of the medical professional bodies in the world would consider it professionally dishonest to offer any form of medical advice as a Doctor whilst hiding behind anonymity, and would likely start disciplinary proceedings over this.
Why would a medical body would have problem with a doctor - who doesn't use his title or name - that posts info on a forum ? he isn't deceiving people in any way , and he isn't using his title in a wrong way.