Yes, mostly based on career longevity. Every athlete has maybe 10 years, give or take, in their profession before wear and tear and aging drags them down. Yes there are exceptions to the rule, but nonetheless, the average is usually 10-to-15 years. Yes, there are some who get endorsement deals and other supplemental pay post-career, but there aren't many Michael Jordan's out there doing Hane's snug fit commercials 30 years after their prime.
HOWEVER.
I'll put the addendum of them having to keep their nose clean and being a strong role model and bending to league rulings. Leagues shouldn't be afraid to spank the million dollar brats just because their bottom line is higher than theirs either. I'm not a huge sports fan, which is why I'm generalizing in my remarks and sentiments, but I've seen enough over the past few years in the news alone to tell me that the athletes need to be wrangled, corralled, and put in their place when it comes to how they represent their franchise and league.
Point blank; if you want to play catch for a living for millions of dollars, there's got to be a give and take when it comes to how you approach those paying you. No player's strikes over a silly skim on your millions, no DUI's or drug busts, and no harming women, children, or animals. You are where you are today because you looked up to someone when you were younger who was in the same position as you, and while there are flaws in all of humanity, embrace the fact that, like it or not, you signed up to be on that Wheaties box to sell a kid some damn cereal.