A lot of basketball players are great athletes who probably chose the sport because it pays a hell of a lot more than pro football does and does not carry anywhere near the injury risk either.
However, while certainly not impossible, the better ones committed themselves to another sport and will likely see it through till they realize they won't make it as pros. You also have to remember that a lot of them can make millions playing in leagues around the world, so at best only a few will even consider pro football.
And proud of it!!!