RFID didn't work reliably from more than a few inches away and with that many items? Tagging every item including bulk things like produce was a non-starter for merchants due to all the extra labor involved? RFID tags cost much more than the barcode already on product packaging? Check out hardware for this was massively expensive, didn't integrate with existing lane systems smoothly, confused consumers, was largely unavailable due to lack of demand, and was super buggy / unreliable?

Those are all guesses but they all seem likely to me.