It was only wildly successful until our leaders "sabotaged" it by forcing it to obey standard actuarial practices. (Unlike the rest of the govt, the USPS is now required to fully fund it's pension plans.)
Also, it's pretty hard not to be "wildly successful" when you get a legally enforced monopoly. Comcast is also "wildly successful", but we certainly don't want to expand that model.
Yes and no. It's a monopoly that can't charge what it takes to stay afloat. Raising prices or changing delivery schedules requires an act of Congress! No member of Congress wants to have to answer for that, so the price of sending a letter hundreds - if not thousands - of miles, to be hand-delivered remains under one-half of one dollar $USD. THAT IS INSANE.
It's been argued, deftly, that even with a decline in volume for mass mailers, raising the price from $0.49 to $1 would not only put the USPTO all the way in the black but enable them to meet obligations for years to come.
That's exactly what every profitable company does: pay their workers less than they otherwise could. The only alternative is to distribute all profit among employees. (And some people who believe that profiting from other people's work is immoral advocate just that.)
See this comment for a more detailed explanation: https://qht.co/item?id=6710602
Also, it's pretty hard not to be "wildly successful" when you get a legally enforced monopoly. Comcast is also "wildly successful", but we certainly don't want to expand that model.