The problem is how low the barrier for entry is. In very short time, any player can be good with a sniper in just about any scenario. On the other hand take fusion rifles for example. They have a very distinct effective range. Punish heavily for missed shots. Require intimate understanding of each model's projectile velocity and recoil pattern. And even given all of that it's still up to chance whether or not the game will give you the kill, or even significantly damage a target. Whereas all Destiny snipers are hit scan. They cripple opponents on a body shot, many take an enemy to within 1 bullet of dying. Most every impact class kills on the revive. The most common models can kill a super from a safe distance. The rewards far exceeds the risk. It's the obvious right choice.