I have never known a practicing (private practice) doc who was not on the phone in his spare time, concluding deals in real-estate, stocks, manufacturing of a product, partnership in a restaurant, or some similar deal.
These guys are 'go-getters' and self motivators.
That's why they're in private practice and not on staff of a University or teaching hospital (although they may be, part-time),
They want to make money. the 'American Dream'. Look at the doc/inventor who makes/sells the modified TENS units (The Rebuilder) for PN sufferers.
But I tend to feel the same way as Glenntaj - less than a kindly look in their direction. More like snake-oil hawkers.