Infertile F1 and F2 Bengal Cats

It is almost common knowledge that the first generation (first filial "F1) male wildcat hybrids such as the Bengal cat and Savannah cat are infertile. Almost all the F2 cats are infertile and some F3's are infertile. This makes the breeding of these cats more complicated obviously.

The question I have is, why are these higher filial wild cat hybrids infertile? In the wild inbreeding between say Siberian tigers has caused infertility. I know that. But I am not sure why cross breeding a wildcat such as the Asian leopard cat and a domestic cat (American Shorthair) causes the male offspring to be infertile.

For the natural processes of an animal to be impaired something has to be wrong - correct? I can only conclude that it is unnatural to cross breed a wildcat with a domestic cat. If it happened in the wild (and it does occasionally apparently) the male offspring would not be able to procreate.

A Google search does not throw up an answer. All the breeders sites refer to infertility in F1s etc but don't explain why.

See an F1 Bengal Cat.