Right. My understanding is that military doctrine is generally to immediately attack when encountering an ambush. Presumably, that will throw your attackers off their pre-planned attack and help you regain the initiative. So you want a big enough defending team such that you can immediately assault the attackers while also retreating with your VIP simultaneously. For the counter-assault team, you want to suppress the ambushers as quickly as possible (get their heads down), thus the automatic weapons.

As int_19h points out, there are special-purpose weapons made for this (see "personal defense weapons") and they are likely what pros carry.