My guess: easier to establish the original owner and limit warranty repair costs. Boxes disappear, but the serial number will tell them when and where it was sold into distribution, and subsequently the hands of one of us. Presuming you register the grill, it's a permanent record that can be traced back when someone calls and says "I need a new lid cause this one's warped". Not that any of us has ever done that. Not at all. No way.