I get medicines by USPS. I could afford to have FedEx ship them, but a lot of people can’t.
The entire problem is that the Republicans decided that USPS had to pre-fund all its pensions and health care costs for 75 years in the future. No government agency faces that requirement; no private sector business does. This was under Bush. If the USPS were permitted to follow generally accepted accounting principles, most of the problem goes away. But Trump would not have an excuse to shut it down.