Maybe since the Marines realize they'll be stuck with it for quite awhile they wanted to make sure they had everything right. Marines aren't known tolerate "Vapor-Ware Snake-Oil Salesmen" very well.
the Osprey comes to mind...
but that is unfair. I know Marines, and am even messing around with some stuff with one, and am *well* aware that if sharp-end Marines are allowed to direct light-arms development, the results are brutal, ugly, durable, idiot-proof, and quite delightfully lethal :)