You're right, I probably don't properly understand the problem they are trying to solve

But with so many possible observers it wont be possible to satisfy everyone about simultaneity of widely separated events. However scientists have known about relativity for a century and they can factor it in to surmise what another observer experiences. If they are going to do that then why not base everything off of the calculated experience of an observer that uses UTC at some point on Earth (maybe Kazakhstan)

Relativity is real, birds no so much

Apparently it was shown working in 2009Costs and reliability have presumably improved since then.

Maybe you were "let go"

I recall the "parallel checkout" being a stated use-case, clearly people's experiences vary dramatically and maybe in real life it works better for fabric items (like socks) than for metallic ones (like cans of beans).

or maybe there was some non-technical factor that hampers its adoption in the US

So they are saying that if they use a clock on the moon their local time will drift w.r.t a clock on earth. Isn't that even more of a justification for using a clock on earth as the reference for everything ?

It's not as if you can't build a special clock that can factor in the timing differences and get a radio signal from earth to keep it in trim.

I thought this was the promise of RFID; instead of self scanning through those shitty slow barcode readers, the whole cart or basket could be scanned in an instant provided products were tagged with rfid.

The only need for the monitoring then would be to make sure RFID tags are not sneakily removed before walking out (a choice of products to sell might help).

Seems to me that most people enrolled in the system are likely honest and mistakes etc. could be mitigated with spot checks. And the blatantly dishonest are shoplifting and probably not enrolled in the system anyway - there would need ot be a different approach to that