[1] https://ips-dc.org/how-congress-manufactured-a-postal-crisis...
Pensions for retired employees are, generally speaking, paid by the contributions of today's employees. No other federal agency has a business that is guaranteed to continue declining in volume and revenue. Congress recognized this in 2006; this is why said law was passed near unanimously. Better a decade of pain, than to not have USPS pensions fully funded in the future.
And as for the private companies that are also guaranteed to be declining in revenue, I bet a lot of retirees of newspaper publishing companies wish that their employers had been required to similarly bulk up their pension plans c. 2005.
First, the USPS as a US service need not be profitable. They were also fiscally sound _until_ the Bush administration abruptly changed the rules of establishing pension liabilities as current https://theweek.com/articles/767184/how-george-bush-broke-po...
And since USPS can't cut unprofitable routes and can't raise postage prices above inflation, again because of legislation, there are only few options left.
Unless the Congress decides to directly fund USPS, or let them raise more money, the cost cutting is the only way forward.