Because some people can't humiliate them enough. From the Charlotte Observer:
Ruth Regina likes to say her business is going to the dogs, but it's actually just going to their heads.A wigmaker to the stars, Regina is now designing hairpieces for dogs -- braids, curls and extensions that can be dyed, highlighted and styled to order for pampered pets.
[...]
She did her first dog hair design years ago for her niece's basset hound, to coordinate with an Easter ensemble.
"The general public for many years were not wearing wigs unless they really had a strong need for it, but now everything has changed," she said. "Wigs are so in. Hairpieces, extensions. It is a very big thing now....I thought, well, why not for doggies?"
Regina has not sold the canine hairpieces yet, although she says she has potential customers, like pet shops, lined up.
She figures that "mommies of doggies" who treat their pets like children will be willing to pay $18 to "hundreds of dollars."