USPS is actually adequately funded. However, a Republican congress saddled them with having to fund 70 years of pensions up front, something that Republicans somehow don't seem to care about when the pension obligations belong to a company like Bethlehem Steel.
In addition, we fund the Post Office in order to maintain connection to those parts of the country that profit wouldn't connect. So, ironically, if we demand that the Post Office be more profitable, the first people to suffer would be those calling for its head. But, then, that's become pretty much standard operating procedure in US politics.
And, historically in the US, a Post Office generally was more than just mail. You could go there to pay your bills, send money, etc. This is an artifact of the Post Office generally being associated with the General Store.
For example, it pains me to see all the "Paycheck Cashing" places that are so predatory when the Post Office could do this effectively for free and make money on the float.