I know several physicians worth tens of millions, few worth more than just tens of mils.
Strangely enough, many of them don't care about the trappings of money really. A lot of them drive beat up cars, dress fairly slovenly. Haven't bought a new home in decades, etc. They have nothing to prove. To them, money is securing their children's future or keeping score. It's amusing to see a doc easily worth close to a 100 mil pull up in a beat up SUV from the 1990s and all the hotshot young docs in their fancy 100k cars next to him.
Now, as to how they got all this money? A number of ways. Right time, right place, very hard work, and good investments.
They did not practice in large cities. They started off at a time when reimbursements were high, worked non-stop with massive patient loads and invested like crazy. Motels, hotels, restaurants, gas stations, vineyards, you name it. Also passive income like surgical centers, etc. They grew their fortune over decades of extremely hard work and being able to work hard at the right time to capitalize on their skills. I know one that has so much damn money (lets just say he operates in the finance world at a whole 'nother level than we can dream of) he's a doctor purely because he wants to be, works a few shifts here and there to keep up and one of the nicest guys ever.
Us young guns still make a pretty good scratch. The power couples are very well off living large. But unless we hit it large with investments or the lottery, or sit on a property for a decade or two and it pays off, we can hardly match these guys.