"Zero Tolerance" is a way of saying "I care so much more about this than others." If politicians really meant it, they would apply that standard to Hollywood, to journalists, to entertainers, and to other politicians. But those groups can cause trouble for politicians, make fun of them, embarrass them, slyly hit back. NFL Players don't have that power - they are easy targets. Charlie Sheen, Nicholas Cage, Sean Penn, Alan Grayson - no tolerance? Athletes are famous, but their power over others is nonexistent.
One group is also whiter than the other, which may also figure into it. Attacking people who can't fight back is a lot of how politicians make their living.