It has to do with effectiveness. Smoke is more effective as a way to hinder the enemy's ability to sight a target. Template weaopns, on the other hand, are shot at actual targets, as that is where they are most effective. Yes, I am well aware that when clearing a room, no one says, "Hey, you - bad guy - catch this grenade!" and then ducks for cover; one would just roll the grenade in and leave the badguys do the yelling. But, to avoid abuse (trying to get the leader by manuevering the template to encompass them, praying for deviation to extend range, etc.), this game mechanic works beautifully.