what causes dental decay in cats?

Is it a certain type of food? genetics ? something else? I am curious because it doesn't make sense that in the wild they'd get cavities or decay but for some reason house cats/pets get decay. I want to do the right thing for my cat and don't want him to have teeth issues. He's 4 years old and his teeth seem fine. He eats wet and dry food every day . So I am curious if it's a certain kind of food or something else that causes the issues.

There is a type of 'decay' in kitties called FORL.  They aren't sure what causes it but it is believed to be auto-immune in nature and my vet told me it was found in the cats buried in the pyramids in Egypt.  It has been with our kitties since probably before domestication.  They simply live with it as long as they can still hunt once they can no longer hunt and eat they die of starvation.  They have found that the lions in Africa that turn into man eaters actually have rotted canines which is why they turned to humans as prey.

Many people brush their kitties teeth.  It's easier if it is started while they are still kittens.

I've had several discussions with my vet about Feline Ondontoclastic Resorptive Lesions, and it is much as Denice said.  It is not linked to genetics, or vitamin deficiency, or any other outside influence that they can determine.  It is indeed autoimmune in nature. 

The way my vet described it, is that it is the same process the immune system goes through when it "kicks out" the baby teeth.  It's a certain "mode", if you will.  Usually the mode is "switched off" when the baby teeth are gone. But for some unknown reason, in some cats, the mode gets switched back on in their mid-late years and they start losing their teeth again. 

I asked my vet if the process will continue when all the teeth are gone, as in, would it move on to affect bones or perhaps nails.  She said no, that when the teeth are all gone, the process will switch itself off again.  It's just the most bizarre thing, and it seems to only happen to cats.