Size is potentially an issue. In card printing, anything other than the standard sizes is considerably more expensive.
I could easily do some "standard" card sets on DriveThru such as: "German Panzer Korps, 1943" or "US Armored Division 1944" and so on. But they'd be 3.5" X 2.5" poker cards, and would dwarf any 15mm bases that were put on them.
In other words, they'd work only for those people who want to use the cards exclusively, and who don't have any interest in using figures... OR for those people using 25mm figures and very large table squares.
I'd also need to give a lot of thought to how the sets would be composed. No matter how I organize them, they'll be "wrong" for most players. For example: if I sell a "Fallschirmjäger Division" pack, then the guys who only want one small FJ Kampfgruppe will complain that they shouldn't have to buy the whole division.... but Hey, where's the Tiger company that I want to attach to it? Do you really expect me to buy the whole "German Corps Assets" pack just to get one Tiger??
If the packs are too large, people will complain that they have to buy a bunch of stuff they don't want. But if the packs are too small, then they'll complain that it's not economically feasible, given the cost of shipping, to buy such small and pricey sets.
Multiply that times the number of nationalities and the number of Periods of the war, and you get a staggering number of sets.