Is the game marked as Private? You do not get card drops while it is marked Private.

How do I remove it from private or how do I know it's private?

whce ji ecot

Right click the game in your library -> Properties -> Privacy

If you mean you already collected your available card drops and now need the rest, you'll have to trade for them or buy them from the market.

引用自 FFL2and3rocks：

If you mean you already collected your available card drops and now need the rest, you'll have to trade for them or buy them from the market.

I think this is the case considering they have cards for the game.