i think it is because American pitbull terriers are a breed unlike wolf dogs (that is excluding hybrid breeds selected for a dog-like behavior who are in majority dogs genetically anyway.)
You need a permit to own a wolfdog in many countries and their breeding may be illegal because unlike dogs (even pitbulls) they lack the several genetic mutations humans have selected for a more submissive and friendly behavior.
There's a reason there are sanctuaries for wolves and wolf dogs but not pit bulls.