People do. They also breed horses that are barely 2 years old. Or rats that are not even medium-sized yet. It's got to be at great expense to the undersized female and in my opinion, it is not good and something to be avoided.
If you are looking for personal experience; I bred my 2004 female last year at 1800-odd grams. I refused to breed her the year before at 1400-odd grams.