That seems less of a problem with USPS itself, and more of a problem with the funding structure of USPS. They are now in the position where they are forced to deliver junk mail to subsidise the loss-making deliveries they are mandated by law to perform.

If the government mandates USPS to perform deliveries for a price that is below cost, these deliveries should be partly funded by the taxpayer. They should not be forced to subsidise these deliveries by delivering spam mail.