I'd pay more for a pack that had more stuff, proportional to the additional animals, plants, scenery, building pieces etc.
I don't know that money is the main reason the sets are the size they are, though. It takes time to design new critters (at least ones that aren't simple reskins) and to create new foliage. Not sure how much time it takes to create new textures for building pieces.
I'd prefer they not make DLC less frequent but larger, if they are currently working at capacity for creating new content. Four bigger DLCs a year, though. I'd be all over that!