RFID tags are way to expensive to scale. The margin for one of the products might be just a few cents, so with RFID tags they might have to sell at a loss or rise prices. This would eliminate the cashier, but at least in germany the wage/item scanned is way cheaper then RFID tags.

Presumably it works if your phone runs out of battery while in the store

When you exit it needs to match the items scanned (with RFID) to your account (using phone proximity/computer vision)