Just based on what I read in the eBay ad, I'd say these were a promotional offer - the kind of thing you'd find in the package, like a toy in a cereal box. I've seen bread companies do this sort of thing for a LOOONG time, including "trading cards" in their loaf bags, and sometimes (as this case appears to be) the cards could be used to play a game.
Tobacco companies used to do the same thing, but they often included collectible baseball cards or standard playing cards that could be collected into a full deck. The rarest baseball card in existence, was a tobacco premium card of Honus Wagner - the production was shortened because Wagner didn't want his likeness used to advertise tobacco products, something he didn't approve of.
Decks like that tend to have a higher value because they weren't as easy to obtain as simply buying a pack of cards at the store and as a result, comparably fewer complete decks will exist.
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