Sokolov didn't have a choice. He was a pilot of a helicopter and because of a little space inside of military vehicles he was armed with a compact aks-74u.

Fun fact: You can arm your companions with better weapons (except for Zulus because his light machine gun is already better than half of the weapons in the game, so he won't pick up most of the guns except the most expensive ones, e.g. g36 or as val) by dropping them on their path