I couldn't possibly see this more differently than you. Your claim that government is so accountable simply doesn't match the facts. I could show you report after report of government waste. Here's an example:
https://www.heritage.org/research/reports/2009/10/50-examples-of-government-waste
I also disagree with your contention about why they don't open another lane at the post office when it gets busy. I see it all the time. A huge line runs out the door and a supervisor walks in, looks around, and then walks away. There is a "not my job" syndrome. When the same thing happens at the grocery store the supervisor opens a checkout lane and pitches in. I can understand why you would love us to believe that people in these sorts of environments are generally just as motivated to do their job well as free market employees (and it would be great if they were), but it's simply not the case. Although there are exceptions, most people make their decisions based upon what is best for them. The post office supervisor knows that his pay and job security will be no different whether he pitches in and does a job he doesn't need to or not. The grocery store supervisor knows the opposite is the case for him.