Why? I can only guess, but engineers think in terms of math - the market is created by human emotion and is not mathematical except by coincidence.
Docs, well, aside from giant egos they generally have underdevolped social skills as a group, which means they don't understand people as well as they think (and markets are created by the emotions, and sometimes, but rarely, the rational thoughts of people) despite dealing with patients, and also tend to think in terms of natural science.
Many people successful in some profession - engineering, medicine, law, etc - think they shuold naturally be good at trading, but trading requires a very different mind and skill set.
Many of the best traders I saw when I was on the floor were former athletes. They're competitive and don't over-think things.
Oh...and I attended medical school also - U.S. MD program...but was a competitve athlete in three sports as well, so maybe that acts as a balance...
