When I was recently looking for a dog I went down to the local shelter numerous times.
Probably 50% of the dogs there were pits or pit mixes.
As I was reading through websites yesterday, I found a few pleas from animal shelters for help placing pit bulls in adoptive homes. The pits were by far the most common dog brought to the shelter (or abandoned) and they were the hardest to place in adoptive homes. Therefore they were the dog most often euthanized.