I'm not really sure what you're trying to get at. The emphasis for track is towards shorter events (there's a name of it - they call it "sprinting") whereas the emphasis for cross country is (obviously) distance. I think you'll find most runners that run cross country also run "distance" events of track. Regardless, everybody has their area of specialty– events their good at, and events their bad at. As it turns out, most people who are good at the 400 aren't as good in the 3-mile (i.e. XC). Some 400 runners still run XC anyways, and some are good, but that's not the general trend. And those track runners/sprinters that don't run XC don't do it because of other sports like Football and Soccer. So really you have to blame those other sports for the reason many 400m runners don't/can't run 15:40s.
I'm not really sure what
I'm not really sure what you're trying to get at. The emphasis for track is towards shorter events (there's a name of it - they call it "sprinting") whereas the emphasis for cross country is (obviously) distance. I think you'll find most runners that run cross country also run "distance" events of track. Regardless, everybody has their area of specialty– events their good at, and events their bad at. As it turns out, most people who are good at the 400 aren't as good in the 3-mile (i.e. XC). Some 400 runners still run XC anyways, and some are good, but that's not the general trend. And those track runners/sprinters that don't run XC don't do it because of other sports like Football and Soccer. So really you have to blame those other sports for the reason many 400m runners don't/can't run 15:40s.