Pic above is the NYC central PO, the James Farley US Post Office. Once a beehive, now pretty empty inside the grand building. A temple to commerce, paper communication - and Christmas mail.
They are communal spaces where everybody goes - or used to. They employ many people who might not be easily employable elsewhere. They lose money, but so do schools, libraries, parks, highways, passenger rail, and the US Navy. Everything governments do loses money. Organizations and institutions exist, in part, to do things that are difficult or unprofitable to do otherwise.
Naturally, whenever large numbers people are involved, politics enters and, at that point, money mainly is about votes.
Why is the Post Office any different?
Well, perhaps it isn't any different. What seems different today is that many government civic "amenities" and "services" have competition from private operations who carry the risk, so taxpayers are less willing to throw their money away to governments who don't really worry about the money.
Parks are operated by operations like Coyote's, libraries have to compete with Kindles, government schools have to compete with charter schools, government rail has to compete with cars and air, and even the military hires tons of private contractors. Despite the massive increase in the size of government, there are more and more people willing to provide traditionally (meaning since the Progressive Era) government services more efficiently, more cheaply, and unburdening the hapless taxpayer of the risk of money-losing services.
What's your take on it?
