A couple of key items to consider: the overhead at the big contractors is obscene. The amount spent on the engineers and builders who actually do the work on the goal of the contract is a tiny fraction of what is spent.

Second: when a small company offers a better solution at a cheaper price, the government picks the big company who spends all the money and either delivers nothing or delivers crap.

Third: take a look at the chart for all the steps in a major acquisition program and you will see another reason it is so expensive.