For NFL players, I imagine its due to the sheer amount of squatting and running they do. After all that hard work, their calves/quads/glutes are strong enough to propel them pretty high into the air.
As for shotputters, I've got zero frame of reference for how high they can/can't jump.
I'd be interested to know what the average vertical leap is in the NFL, NBA, MLB and AVP (volleyball)