This is actually a bad idea with how the military is presently structured (Also, the military has always used contractors to supplement in support roles from manufacture to administrative going even back to the Revolutionary War). The core issue is though that the military constantly rotates soldiers between locations and assignments on roughly a five year basis. While this makes a degree of sense for overseas deployments, this is also done for all home stationing too, which means that for many non-combat support roles you have a constant churn of soldiers who are coming and going from an job. This means that many support functions of the military end up depending on contractors who stay on certain activities long term to build and preserve institutional knowledge. This is especially present in IT areas. It's one thing to move from being a maintenance engineer on one base to another, the skills transfer, but for IT matters you don't really have equivalent postings and due to how IT infrastructure is managed you basically have people rotating in and out from a single point, thus preventing the military building up institutional knowledge for how to run and manage such things.
Contractors also tend to be cheaper than forcing everything in house, and there's actually more accountability with contractors, as their contracts are for explicitly lengths of times and then rebid, which means they are in constant competition and have to reliably meet their job requirements or else the contractors will be dropped. Is politics involved? Certainly, but politics would be involved if things were purely in house and there would be LESS public oversight of things...