Your comparison stands true for a lot of entertainment orientated people - singers, songwriters, actors, screen writers etc etc etc all get paid more than the average university professor.
But the reasons are easy enough to uncover - a university professor can never come close to the audiences that pro or even amateur sports athletes can generate. When was the last 90 minute long lecture that commanded 50,000 seated attendees, a televised audience of tens of millions, and a further extended audience of hundreds of millions? Not even the recent series by Neil deGrasse Tyson can command those sorts of figures...