mechanics aside, i don't think soliders fit, thematically, within gamma world. soldiers are often more of the organized sort... that doesn't seem to be the type of creatures in gamma world where it's lawless chaos (almost).
whether or not there was also a mechanical reason to do so (such as speeding up some combats) that may or may not be true. but i think it might have just as much (if not more) to do with the flavor/appropriateness of the role in GW.