If they didn't (have babies) there would be no more midgets.
Midget is a derogatory term. The correct term is dwarfism. And,
you are wrong. Dwarfism can and most often does happen in families where both parents are of average height. It is often caused by one of over 400 skeletal dysplasias. These affect bone and cartilage growth, and often lead to disproportional short stature. The most common type of dwarfism is achondroplasia which occurs in about one in every 40,000 births. There are an estimated 30,000 people with some form of dwarfism in the United States, and 651,700 in the world. There are a lot more dwarfs than one might think. There are 14 different types of dwarfism.