I have no idea how long it takes to take an animal from scratch and get it ready for release. I suspect, but could be entirely wrong again, that time was put aside to fix bugs/improve the game in the months after release. Which is exactly what has been happening.
I assume there is some cross over of staff doing this that would be needed on DLC also. Does it mean this is set in stone going forward for DLC size, who knows.
I am pleased with this DLC so far and will see more when we know exactly what is released in it. Would I always want more, probably yes. Should I expect more, maybe in the future which I am sure we will get.
Ask yourself, would you have sacrificed the last 2 patches and the one coming up for a DLC double in size and quantity. I don't think I would. Also there is a bit of a virus going around which is probably affecting productivity as well to some extent.