You are being too nice calling it a habit. Breeding behemoths is what sells. People will pay a premium for the pick of the litter (which is code words for "the biggest"). I don't have any problems with dog breeding per se, but the market forces are seriously broken.

EDIT: In addition to pushing for bigger dogs, it's also profitable to drive down food and vet costs. Kennel clubs like the American Kennel Club are scams. The kennel clubs just receive fees for processing paper. They don't inspect breeders. They don't care if you're a puppy mill. As long as you pay your fees, you will get your papers.