I guess maybe you haven't enabled electronic statements for your accounts or something, but for me 99% of what I get from USPS is junk mail or online shopping deliveries. Not clear why either of those need to be subsidized.
When people talk about International Mail being "subsidized" they're talking about EG treaty negotiations with China that force the USPS to receive international packages from China at significantly below cost. They then have to pass those costs onto the US consumer.
I've not seen any citation which claims the junk mail part of the USPS is unprofitable.
To be clear, I hate junk mail. I've just seen this claim made a few times without citation.