Oh I suspect they all merged into one big shipping co. already, they just haven't told us.

Trying to have like 10 Ebay/Etsy type purchases delivered to a business in rural northern CA (border of Lassen National Park) for someone recently, it was chaotic trying to track them. Turns out there is all kinds of mishmosh at that level, UPS and USPS definitely merge, share routes, tracking, delivery. For example, there is this new thing called UPS Surepost hardly anyone knows about

https://www.ups.com/us/en/help-center/tracking-support/sp-definition.page

UPS SurePost® is an economy, residential, ground service.

This service combines the consistency and reliability of the UPS Ground network with final delivery typically provided by the U.S. Postal Service.

Note: UPS My Choice® Members can upgrade a UPS SurePost package to UPS Ground for an additional fee. Once upgraded, Members can use the features available with their Membership to reschedule or redirect delivery to an alternate address or to The UPS Store®. Upgraded packages typically arrive one day earlier.

And in communication with  an Ebay seller the other day, along the lines of "where is my package?", I noted upon reporting that the package had been delivered even though tracking said it hadn't yet,  that deliverers seem to be getting sloppy about scanning in tracking recently. The seller agreed and added that the sad part of this for sellers is that Ebay duns them if the proof of delivery doesn't come in. So the Ebay system is in on all this, too...