For some reason, in the US it is more politically acceptable to pay a private firm $200K per worker for a government contract than it is to pay $150K per worker to hire people to do the job.
Because in aggregate the US believes in private enterprise above all else, to the point where we will hand de facto monopolies to cable television providers or mandate the purchase of health insurance from private companies (and only from private companies) before we'd ever stomach the idea of having government get directly involved in anything.
And this is not a partisan thing
Just because it's not "partisan" doesn't mean it's not a decidedly right-wing idea. And it was most certainly a partisan idea until Ronald Reagan won the most lopsided presidential election since 1792, at which point the party of Roosevelt and Johnson had to start positioning itself as "Republican Lite" in order to start winning elections again.