Most guys don't play anywhere near that long.
Usually waste 4 years at college, and few would be on top money straight away.
Keep in mind that until recently the salary cap was $1M, and whilst some guys are now getting much more, we don't know how sustainable that is.
Do they earn more than your average Joe? Yes, but not enough to retire after 10 years.
In my observation, even those smart enough to accumulate a nest-egg, make a couple of mistakes:
Too often they invest that nest-egg into a business, that they have no real idea how to run. Eg a retail shop, or cafe, etc.
I recall a certain famous Wildcat, who nearing retirement, and despite a LONG career, was basically broke because of failed businesses.
The other one is that they slide into sub-optimal employment, such as running a shop, or working for charity, not realising how quickly that nest-egg will run out.
In my view the smart ones are those who decided on a 2nd profitable career, and make the transition early. Haven't come across any ex-Wildcats, but I have worked with several ex-Eagles in the Mining Industry.