While everything else you said is true. This is just silly. The reason cards are used to make money is because those buying it.... are crafting badges. If badges weren't being crafted, cards wouldn't be selling. Period.
It should be silly indeed, but I believe all the card thing has became somehow a currency/barter method.
Like in buying low -> trying to sell high, and so on.
Anyway, un-scientifically speaking, I'm getting way less boosters (and selling less cards) than just a couple of months ago.
Call it market saturation, call it whatever you like, but it seems to me that way less badges are crafted nowadays (compared to this summer, when it was a novelty).