I think it's the same in many sports and just comes down to awareness... some guys just know what's going on around them and others don't. I play Ultimate, and I can usually tell the people who've played other sports growing up because they tend to have an awareness of where others are on the field and that sort of thing, where some people are just clueless and always running into other people, or cutting people off. I could see the same with the better route runners just knowing where the defenders and open spots are. Some of it is from film study, knowing the other teams' tendencies, but a bigger part in my mind is that field awareness. Ellingson, Schoen and Demski seem to have that awareness in spades because they are very good at finding the holes.
The part about running a route is the difference between being able to do a head fake and then a sharp 90 degree turn vs. just running a slow arc. The crisp cuts will get you open, where the lazy arcs will make it super easy for the defender to stay with you.