Why doesn't the MEC (normal) or the Spetnaz use the Ak-47? The Russians invented the AK-47, so that should be their Assault + Medic weapon because the Ak-101 sucks. The PLA can get some different weapons. And Why don't the Rebels+Insurgents use ak-47s? All Insurgents ever use are Ak-47s, because its the most produced weapons, and it does some pretty good damage (it's probably the only thing they can afford too)
Because DICE is stupid and doesn't want the game to be accurate to what the real world army would use.