An interesting perspective to consider, is that the original breeders may not have seen it as a deformity; as opposed to simply creating a desired shape.
Yes, you could point to the mouth shape as being an obvious deformity, but whether or not that was the original intention won't be known since the original creation of BP's is either unknown, or a closely guarded secret.
For example, some of the goldfish varieties which struggle to swim etc, the Japanese breeders don't tend to think, "hey, I'm gonna create this retarded goldfish for a laugh Joe", they legitimately think they are creating something beautiful. Which it is, depending on your point of view.