How much did their education cost? At least in the US, doctors don't make that much after student loan payments, insurance, etc.
In England* there is a cost (£9250/year), but it's slightly misleading to think of it like that because of how Student Loans work here.
You pay nothing on your Student Loan up to a certain income (£25k, or $33k), 9% past that point, and then the remainder gets forgiven after 25 years. So in practice, it's an additional marginal tax rate for having gone to university.
(* different elsewhere in the UK - e.g. free in Scotland)