That's usually because hunters are prohibited from using suppressors. Subsonic ammo isn't ideal for big game because you do have a a reduced range and speed. And because of the NFA, every suppressor needs a 200dollar tax stamp and several months of waiting, this also drives up the price of suppressors. In PA they tried to pass a bill to allow deer hunters to hunt with suppressors, but it was voted down because you don't need to know things to vote against something.