You can search for
Regional Transportation Optimization, if you want to get down into the weeds. There has been ongoing coverage at
https://www.savethepostoffice.com/.Locally, we lost afternoon pickup of outgoing mail leaving our town a few months ago, so now the truck that delivers the mail to our local post office at 8:30am also picks up the prior day's mail and drives it to a regional center 150+ miles away. In the past, a truck came back through town at 4:30pm and took that day's mail south 70 miles.
This has been rolling out slowly since 2021. If you wanted to imagine a conspiracy theory relating to mail-in voting, you might posit that minimizing the importance of the postmark may be another way to allow ballots to be printed days after the election.