Yorkiepuppie, you make some good points and asked some fair questions. I'm not sure just how scientific of an answer you'll likely get, but I can give you some my reasons for not breeding for tinies. In no particular order....
1: It just isn't necessary to breed for tinies. Standard size Yorkies can and do produce occasional tinies.
2: It's dangerous for the mother. The risk of c-sections is high. Complications of any sort can be more dangerous for a smaller dog just as any illness can be.
3: Small mothers have small frames. They are delicate and I don't think it's right to put the added weight of babies on their little bodies. To me, it's just asking for joint problems.
4: Qualified homes for tinies are hard to find. For that matter, finding good homes can be a challenge for any breeder. It's just that much harder for the very small ones. Even after you become an adept breeder, finding proper homes is a constant worry and the worry factor goes up for the little ones.
5: If a health issue does come up in a very tiny dog, it is immediately more dangerous due to its small size. The little ones have so little reserve and can have more reactions to vaccines, anesthesia and even blood draws can be difficult. Plus, finding a good vet for the little ones isn't always easy. The risks from a hypoglycemic episode go up as the pups size goes down. How many new owners are prepared for this? Even short-term diarrhea will put more stress on a tiny. De-hydration can come quickly.
I'm sure there's many more that others can add. It's late and I'm probably missing obvious things. The thing about this discussion is what do you mean by tinies? To me, a tiny dog is around 3 pounds but here we've seen mention of 1 1/2 pound grown dogs. Why anyone would want something that small is beyond me. I think you've posted that you have a 3 pound dog. Can you imagine one half that size?
Well, not too scientific, but that's the way I see it...at least at 3 in the morning.
