I've never played a Zynga game so I'm just guessing. I think this is about (probability of getting an item) = (probability of getting the item for free in a dr

I've never played a Zynga game so I'm just guessing. I think this is about (probability of getting an item) = (probability of getting the item for free in a drop) * (1 + (probability of a user gifting an item to a friend) * (average number of friends)). So for the late items, they pushed down (probability of getting the item for free in a drop), so you were unlikely to get it in a drop or as a gift from a friend.