Easier to do when you're an extremely relevant person in your sport.
Not all NFL athletes have a shot at getting any endorsements at all. In fact, most don't.
Be a star player or famous role player on a very successful team, that's way different than some backup lineman who is out of the league by the time their rookie contract ends.
American football is by and far the worst culprit - in all the other big or semi-relevant american sports - baseball, basketball, hockey, etc, you can make a decent living playing overseas. Not huge, but decent enough. Can't do that with football.
100% agree with you. Median salary is $800k, which is amazing, but if you only get 2-3 years out of it, need to index the take-home and live like a college student to make it worth anything after compounding.
Think about these fantasy sports gambling apps, your coworkers who distract themselves from the drudgery of work by discussing sports, the financial institutions that take a transaction fee from money being passed around, the infinite scroll of content on social media, all because of athletes.
Not me, I spend nothing and invest it all, but all these investments are basically leveraging what society truly wants, among which is leisure and art.
Functionally, as a curmudgeon, my value to the economy is near zero.