While none of this is codified, TrackloX and CX courses are often different. CX courses tend to have tighter turns, narrower lines, and less room in general for passing and riding abreast, while TrackloX courses tend to be more open. And because TrackloX courses often require fewer dismounts, the bikes aren't shouldered as often or for as long (drop bars offer a big advantage when carrying the bike). Also, the pulling leverage that you get from a wide flat bar comes in handy when you're overgeared for the climbs. That's my take on it, anyway.