I think this is largely due to the fact that CTF by definition has a point to which the player is always drawn; the enemy base (when you don't have the flag yet) or your own base (if you do have it). You will of course need to hunt the other player(s) especially in duels; but you can't stray too far from that base either or else you will never score. Therefore in CTF it is a lot easier to predict where someone is and thereby find and fight him. In battle levels on the other hand, especially those with more than one carrot, the enemy could be pretty much anywhere and thus finding him can take a lot more time.