Black ops shotgun vs semi-auto AR?

What are the advantages of using a shotgun over the FN FAL or M14? They are both semi automatic. Shotguns are one shot kill CQC while the semi-auto ARS are two. It's only a difference of one shot. Why does everyone say that shotguns are good at close quarters and FN FAL and M14 suck at close quarters when its only a difference of one shot? Also, FN FAL and M14 are beast at medium/long range, so overall wouldn't the semi-auto ARs be a better choice? They are great at long/med range and only a one shot difference short range. Shotguns however, can't even shoot long/medium so other than the one shot kill CQC they have nothing else going for them.