I don't disagree with you. Obviously a doctor can bring in a lot of money. In the same a stock can be valued as the sum all future cash flows w/ a discounted cash flow analysis, a doctor's future income can have a quite high valuation.

That being said, one accident or illness that strips away that doctor's ability to earn, leaving them in a soul crushing amount of debt that can't be discharged via bankruptcy. Their debt obligations are real.