If all that's necessary is ordering these from WD, what's stopping newegg and the like from also stocking them? I don't really get why they're trying to move in on this market.

Sure it probably doesn't take a ton of extra work, but I also don't imagine many random consumers are going to think to check frame.work for their Steam Deck upgrade HD. And I doubt there's much overlap between people buying a new laptop and trying to get more Steam Deck HD space. A few people accidentally buying this drive for their framework seems like it'd make the negatives outweigh the positives.