In addition to what others have been pointing out, I think the government is also frequently being forced to be penny wise and pound foolish.

I remember reading here a few years ago that one example of this is how writing the proposals for big projects for which construction companies than put offers have to be outsourced because all experts have been fired by the government. This apparently frequently leads to the government getting a much worse deal than anybody else would. I think another thing that happens is that do much oversight gets added that all costs explode. You can't iterate on anything because if the first version isn't perfect it surely was a waste of tax payer money when you need to go back for the next iteration. So you better have several committees and a long proposal process to make sure everything is perfect and no money gets wasted. Great example is the TSA iPad app for random screening selection that was a big topic a few years ago. The app randomly showed a left or right arrow and and cost millions to make if I recall correctly. I think the government being inefficient is somewhat of a self fulfilling prophecy.