Well since you asked. . . Military (including Navy) gear originates with a requirement or needs statement. The Program Managers take those requirements and create a specification which details just exactly what the gear needs to be able to do. Sometimes the gear is absolutely wonderful on a battlefield because it's tough and never fails when you need it; but it sucks when not on a battlefield because it's also heavy. Unit cost is also a consideration, but even the lowest bidder needs to meet spec -- theoretically.

I usually stay away from MilSpec because for my needs mountain climber and hiker spec is better -- I plan to stay away from battlefields and I'd rather have something that blends into my environment. I don't buy the milspec Camelbak packs because they scream military and they're a bit heavier; the lighter bags are tough enough. I bought a Maxpedition bag and initially used it as a BOB, but it's heavy for its capacity so I went to a much lighter bag that blends much better.

With all the gear that a typical soldier wears and carries, weight is becoming a critical spec in a lot of the military gear, but that Maxpedition bag was way overbuilt for my needs.