Why is pig Latin called pig Latin?

Answer 1

"Pig-Latin" is also known as "dog-Latin." The animal reference is dismissive, and any animal would do. It might as well be "horse-Latin" or "cow-Latin."

Another view:

Actually the term "dog Latin" usually refers to mock Latin, a jargon that imitates Latin words and forms; a famous example is the pseudo-Latin translation of "don't let the bastards grind you down", Illegitimi non carborundum. The name "pig Latin" originally referred to the same thing, but now means specifically the application of a simple tranformational rule to purely English words and phrases.