I am not up to snuff on who carries what but in the show they did say that they were brought to popularity due to the recent more urban environment we are fighting in, in the middle east. Well maybe not urban but villages with buildings. Instead of:
A. Blind firing into a doorway
B. Attempting to quickly about face, asses situation, then fire
the corner shot is used.
What I was getting at is they all have their place. Shotguns are used in combat today, one may argue that isn't not practical to carry that either but people still do.