Contractors are doing non military type work and this frees up the GIs to actually fight. For example take grass cutting on base. Back when the military had almost 3 million troops we had tons of GIs so we cut the grass and did all the custodial work in the offices.
That is not the case now. You don't have the bodies to spare to do non military work like cutting grass. It's cheaper and makes more sense to pay a contractor to do it.
Get rid of the contractors and you have to pull people to do these details. The grass would be cut but that airplane, tank or ship will not get fixed.
The equipment wouldn't get fixed either since contractors do most of the day to day maintenance. GS civilians are another matter. There's bloat there and there's LOTS of useless PC crap that gets forced on the troops training schedule that could be eliminated saving time and money.