system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come the US Postal Service is going out of business despite a huge rise in online shopping culture?
gpt
The financial problem it faces now comes from a 2006 Congressional mandate that requires the agency to “pre-pay” into a fund that covers health care costs for future retired employees. 

Under the mandate, the USPS is required to make an annual $5.5 billion payment over ten years, through 2016. These “prepayments” are largely responsible for the USPS’s financial losses over the past four years and the threat of shutdown that looms ahead – take the retirement fund out of the equation, and the postal service would have actually netted $1 billion in profits over this period.

If any business in the private sector was required to do this as well, it would go bankrupt very quickly.