The short version: people give a crap about what a show chin looks like and how healthy it will be in the long run. In a pet store/animal broker scenario, they're only concerned with finding someone to give them way too much money for any chin they can get "on the shelves".
My pet chins look pretty darn awesome in part b/c I keep them a lot like breeders do: not a lot of treats (rose hips twice a week), wood toys to chew (to keep their teeth healthy), fresh and long leafy hay (to wear down their back teeth), a buddy where appropriate (one is less social), two baths a week in Blue Cloud dust. And while one of them has an impressive family tree, he's the least showable of the three based on size and over-all shape. The pet store chins that bred my first standard male might have been from one of the AWESOME ranches in Ohio, but I've no way to tell, and *because* I have no idea what his genetics are like, I will NEVER breed him. Period.
A lot of people that buy chins or "rescue" them for $100 off of Craigslist don't have that understanding, and go ahead and breed any chin they get, either accidentally by not knowing how to sex them properly, or intentionally to "make a lot of money".
A lot of pet chins (like the one on the Mazuri pellets bag) look unhealthy because the people that own/market them haven't done the research keeping an exotic pet really requires, and the chins suffer for it.