CBS News:
The 2006 law also mandated that each line of business within the postal service set its prices at least high enough to break even. In other words, for the postal service to lose money on package delivery would be against the law.As mentioned in the article, their problem is pension and health costs.
Under a 2006 law, it must pre-fund 75 years' worth of retiree health benefits. Neither the government nor private companies are required to do that.They would be even worse off without Amazon business.