When these guys were playing salaries were tiny by comparison to what players are paid today. And the long term health effects of playing the game at NFL speed and in modern equipment were not known. You think this guy knew if he played he would be crippled for life? The NFL and owners have made a hell of a lot of money and they can do right by the players who helped them make it.
Why do you think all those rules changes protecting players have been made the last couple of years? Because the League knows it has to change and do more to protect players' health.