Because the life of a NFL lineman is so hard. Eat whatever the fuck you want, do some short sprints each day with lots of rest time, and get paid millions to do it.
Or your knee is injured after a couple years? We'll pay you a couple more years to try to heal up, since a 350 pound monster like you will recover from serious knee injuries.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood..."
Respect any man with the balls to fight for your entertainment.