@minerrale @vothnthorvaldson
First of all, it's just a business. It's an appropriate investition to spend additional resources on animals, which are proposed to be a pets, to keep them in a good condition. Customers tend to buy healthy and good-looking pets more likely, so it pays off. But as far as I understand, it's not important for successfully selling animals, proposed to be a food. Thus, if the owner of pet shop will spend surplus resources for maintaining those animals in better condition, than it is required, they will not pay off. There will be wasted resourses, so the pet shop will just decrease its competitiveness.
Besides:
it is a psychological defense. It is easier psychologically for people to treat such an animals like that. Because if people will treat them like a living beings, they will feel more empathy to them and will be more sad, when that animals will die.