Please stop repeating this lie, granted it is repeated enough on alot of hate sites. For you it was probably a mistake since you did not know the truth.
Congress want to protect the taxpayer from having to take over the duties that the USPS said they would do,back in the 70s, the postmaster general and the postal unions want to make the taxpayers pay for their poor management and keep things as they are.
The postal accountability law,2006, requires the USPS to actually do some proper financial management and dropping it would not make them competitive again; even ignore the money they owe for this they would of lost money for the last couple of years. Without the money set aside they would not be able the meet the obligations they agreed to back in the 1970s and the people who retiring now would not have the monies that they are suppose to get.
BTW the 75 years is number of years that is for ACCOUNTING purposes they have to figure future liabilities. It is NOT how long they have to fund benefits. That 75 years of accounting is followed by the DoD, social security, department of Housing, etc