It's because those foods are feline junk foods, comparable to human fast food in health concerns. You can supplement all the vitamins you want, the the foods contain ingredients that do not belong in a carnivore's diet.

As for those top-of-the-line brands: only some vets and the companies think they are top of the line. Many of us actually look at the ingredients and the ingredients aren't that much different than store brands. For instance, cats do not need corn. Why put it in there? As a filler and cheap source of protein. My idiot former-vet was angry that I wouldn't fee Hills (he sold it) but I stood my ground.

Some people use Hills and Iams with success, but my cats have had issues with corn and wheat in the past and I try to stay away from it when possible.

I have a cat that could eat anything and live. The other cat has had kidney issues (an other health issues) so I feed the good stuff. It's actually cheaper than vet bills. Plus kinder to the kitty.

The more expensive foods rely on real meat for the prime ingredient and not on meat meal and garbage along with grains that are not part of a cat's natural diet.

the "good stuff" is seldom found in places like PetSmart and never in supermarkets or grocery stores. I have visited local animals supply houses, feed stores, and garden shops for premium cat foods.

I also feed my fellas cooked meat as a treat. It's safer than the kitty treats.

Anne