There are 2 important points here 1) these doctors are top of...

There are 2 important points here 1) these doctors are top of the tree and are likely to be independently wealthy , particularly those in US. They would not be overly excited about a bit more wealth creation. For them their clinical and scientific reputations are worth far more. Being published is far more important for them
2) the conflict of interest is so massive it is not worth their while holding a significant holdings in the company. Imagine the disclosure to the patients and heaven forbid if there is any litigation, such a conflict would make the cases indefensible. You will note in all the published papers, they would disclosed their affiliation to various companies are disclosed as having being paid retainers rather than shareholders.
I am far more disappointed that Wayne excluded, the rest of the board are not buying but instead asking for options at the pointy end of the business