Created as a department of the new Federal government it was controlled by Congress. Where they took pride in the United States and wanted post offices in every community to pull the country together. They wanted the post office to be the grandest, show permanence and trusted.
Times have changed. Congress can't put riders on bills to add decoration to the simple and frugal design created by the Postal architect.
Now the conservative Heritage Group remembers how back in 2008 the USPS wanted to become more efficient. Close some post offices, stop Saturday delivery, etc. But Congress refused to act. Read the report on how they need to follow what was recommended in 2008