There's definitely something about the collectibility angle that hits different - they come in tons of colors, sizes, and limited editions, so there's always another one to hunt for. That scratches the same itch as collecting anything else, whether it's trading cards or aquarium plants (I get it, I've spent way too much time hunting down rare stem varieties).
The folklore part comes from how it spread through social groups, especially kids trading them at school and posting about it online. Once something becomes identity-tied like that, it doesn't really matter that Stanley has been around forever as a worksite brand - it's become this whole social currency thing that'll probably stick around for a while, or at least until the next collectible craze takes over.