They could have done bonus cards but a bonus sticker would have cost too much for such a limited item. I don't think anyone would have wanted these to have any additional cost.
I nixed the OLDS bonus sticker idea in favor of the wrapper as I didn't want the OLDS base set to have a sticker that was limited to 500 which would have meant many collectors never owning it. Wrappers, uncut sheets, binders, posters, etc are the types of items people are more selective to own so the lesser number works for them. That, and the wax wrapper is da bomz, boy!