That CAN be done under certain conditions, but unfortunately the political discourse of the time makes that politically expensive. For example, vice president Al Gore gave an award to one particular company and presented them as a case study of efficient and effective government contracting. He was right, they did a good job.
A few years later, when the Bush administration needed to have infrastructure rebuilt in Iraq, they turned to the same company. Since they were known to be good and they were one of only two or three companies who could quickly accomplish projects of that type, they got an efficient deal - here's what needs to be done, and here's what we'll pay, now get started. (As opposed to 4 1/2 years for just the bid process). For the next ten years, those who voted for Gore vilified Bush for hiring the company Gore presented an example of excellence, Halliburton. It doesn't matter how good and how efficient they are, people will vilify you if you don't waste half the money on a thousands of pages of bid documents over several years, followed by tens of thousands of pages of oversight and compliance.