You are right. Hand guns are responsible for most of those Chicago, Detroit, and New Orleans murders. Not the people using them.
They want every gun. Rifles are devastating long range weapons, shotguns are terribly destructive, handguns can be easily concealed.
I'm guessing a good many of those murders are defensive use of firearms on very dangerous streets. The shooter then walks off knowing he won't be believed and doesn't want to attract revenge from the deceased's homies.