The answer is simple. If the Government allows the USPS to fail, and therefore become privatized, and therefore bounce back....then it will be proof that the private sector is a better option than the government option and it can be for other areas too (Education, Healthcare, Business, etc.). Basically it's further proof that when the Government gets out of the way, people and the country as a whole, thrive.
Bureaucrats in DC know this. They know that a successful privatization of the USPS could be the first domino.