Here's why:

* Hybrids: Zedonks are a hybrid animal, a cross between a zebra and a donkey. This means they are the result of two different species breeding.

* Infertility: Hybrids are often infertile, meaning they cannot reproduce with each other. Zedonks are typically infertile, further preventing them from establishing a separate, reproductively isolated population.

* No Natural Occurrence: Zedonks don't occur naturally in the wild. They are only created through intentional breeding by humans.

* Species Definition: A species is defined as a group of organisms that can interbreed and produce fertile offspring. Zedonks do not meet this criteria.

Therefore, while zedonks are interesting and unique animals, they are not considered a separate species but rather a hybrid animal.