I think that it can be explained with S & D. Billions of people turn on their TVs to watch footballers, the demand for football is huge. However, there is only one Lionel Messi, supply is low. Doctors are relatively homogenous, and the truly exceptional doctors are also on astronomical salaries (in the private sector).
Also, bare in mind that not all footballers are on £200k/week salaries, that's a tiny minority.