I see your point, I do. But...
It's also important to bear in mind that being a professional athlete is NOT usually lucrative. The mean salary may be high, but not the median.
These guys gamble quite a bit with their chosen professions. To take the bloated MLB salaries as an example - for every Alex Rodriguez with a ridiculous quarter billion dollar contract, there are 1,000 guys making $20,000 a year in the minors, trying to scrape by for their family on the road.
Or how about the NFL, where for every Brees there are 100 reserve linemen making 1% of his salary over an average of 2.5 years in return for a lifetime of medical bills?
So, put yourself in the shoes of one of the superstars. You are THE guy who overcame the odds to become marketable. And you're going to turn down a single cent of your new contract over some misbegotten principal on your profession's relative social value compared to a fireman? I think not.
EDIT: I'm not using "you" to mean "Beerball", rather all the people who spit on these guys for their contracts.