1) NFL knew about the risks and hid them and in some cases deliberately deceived the players about said risks. I seem to recall that only a couple years ago the NFL told the players that with adequate rest, there will be no long-lasting effects from a concussion -- something that has been shown to not be the case.
2) The NFL will go after anyone who releases medical research raising questions about football and CTE. And I don't mean just refuting the evidence, they've gone after the doctors and scientists personally
I don't fault any player in the NFL for wanting the fame and fortune, or playing. But they should also receive all the information that's available as to the risks and dangers associated with playing so they can make their own decision.