because they're still on version 0.2 basically. this is not much more than the tutorial portion of the final game. like playing a WoW character to level 20 and asking why the mechanics are so basic, i think. i expect them to keep adding complexity onto the combat system because it's so easily extensible from this point. they've already showed this with the new armor set they dropped in unannounced the other day. expect things like monster attack patterns to increase in complexity as they add new combat mechanics.