Well, we obviously can't know how many of the boxes have been thrown away, but that is not the primary/only environmental concern. The production of these boxes is already wasting ressources. Also look at the packaging of all other Apple products, even those that are way more expensive than a SS Watch: all cardboard, no plastic in sight; yet the packaging is still nice and clever enough for a "premium" unboxing experience. I also don't think the price of a SS Watch is that much higher than that of an aluminium Watch, making an artificial "premium unboxing experience" unnecessary IMO; for that you have to go to the Edition, which seems right to me. All of this "shiny box" stuff was obviously a result of Ive/Newson aspiring to closely mimick the traditional (expensive) watch industry, back when the AW was presented as a fashion item first. This has fundamentally changed as the demand (and hence marketing) quickly turned to the sportive and other functional aspects. That's also why the aluminum Watch is now way more prominent in the marketing than the stainless one, whch is exactly the opposite from the very first AW; back then Apple even called the aluminum Watch the "AW Sport", marking as a niche model/use case vs the "normal", stainless AW. Hell, even the 149 USD bands like the leather and milanaise loops and the classic buckles at first came in those shiny white plastic boxes, another sign of the misjudged aspirations of Ive/Newson wrt the fashion/premium aspect of the AW; the most obvious sign of those were the gold/rose gold Edition models, a pure vanity project of/for the designers and the only time when I honestly thought "Steve Jobs would not have allowed this".
Btw, for me personally, I much prefer the stainless AW and have bought many of the pricier bands, because I do appreciate the more premium feeling of the materials. I just don't care for the shiny box.