I am sorry to vehemently disagree, but the smartest people do have multiple (as in a lot of) intellectual interests. That just comes with the high IQ territory. Some of them are also diagnosed as ADHD by some less intelligent people.
Medicine is a "calling" mostly for people who are not good at other stuff. In many specialties, a doctor can get away with an intelligence level that would disqualify them as an engineer or real scientist. Of course, medicine is much more than just applied intelligence, but the only reason it used to attract the best and brightest was the income level. And they only used to work much more than nowadays because they made incredibly more money.
No other country comes even close to the average hours worked by American doctors, even now, with all these "young and lazy" generations.