Why make a non generic airsoft gun when you can have 100 non generic normal guns. Airsoft guns can't really even kill unless they have are above 400 FPS.
They can't kill unless they are above 600 FPS, and even then it's sketchy.
Airsoft guns are designed to emulate real guns. In video games, we can already emulate real guns, why the hell would we make a gun to emulate a gun to emulate a gun?