Probably because too many people have accidentally packed loaded flare guns on the plane. A loaded gun is only dangerous if someone uses it. A flare gun probabl

Probably because too many people have accidentally packed loaded flare guns on the plane. A loaded gun is only dangerous if someone uses it. A flare gun probably doesn't have much in terms of safeties so it has a better chance of going off and starting a fire. A single bullet isn't going to do nearly as much damage if the gun somehow went off on its own.