I think what crushed USPS’s finances was a change where they had to account for future pension obligations in their current spending.

One can argue whether this approach, which is followed by no one either in the private or public sector is appropriate (I’m torn. I see the benefit of this change), but what isn’t arguable is that the way it was implemented, falling on USPS almost immediately without a gradual transition period, was ridiculous.

It forced USPS to make decisions that were harmful in the mid to long term, solely to meet an accounting change.