I can understand why there are no rocket launchers that just defeats the purpose of grenades and seems like an overly expensive way of destroying your enemies... however shotguns I could see and the last guy who commented saying 2d animations, they have automatic fire that simulates a shotgun pretty well so I don't think it has to do with that.
Shotguns I think should definitely be added to the game and possibly instead of using perception like other guns it could also have a duality much like melee does with dex/str. Since shotguns have the unique ability of just point in the enemies general direction. Maybe it could be an option for per/dex or str. For all those super str metal armor men out there. Or for people who would use agi/dex. It would give them short range and mobility, while offering a chance to use throwing weapons. A sort of ultimate crowd control build.