It was never about saving money. It was always about dismantling the government so that the oligarchs could carve out their own personal fiefdoms out of whatever's left.
They buy it because they are easily spooked by long words such as 'Pasteurization' and probably fell asleep during the class that talks about all of the diseases that the Pasteurization' process is supposed to prevent.
There would be no reason for them to keep a free service like that when they could charge the consumer for it instead.
No company in position to purchase the USPS would have any conviction to show goodwill towards their users. Only quarterly profits matter.