When did that start? Recently?
See Figure 1 at: USPS Report from 2000
According to that chart, the USPS has been running deficits of a few billion dollars in most of the years going back to 1972.
2006. Get rid of the requirement and a lot of the USPS’s problems go away, at least to the point where it is not an immediate crisis.
It's a cycle ~ once you get to the period where they bought an incredible amount of automation equipment the deficits were supposed to run for maybe 10 years, then disappear ~
Alas, the Great Obama Recession came along and business collapsed, and with it printed advertising.
Jus' the way it is.
USPS can cut several billion dollars in costs but Congress as prohibited them from doing so.