I think cats would be too dangerous. I've had some bad run ins with house cats requiring stitches. Imagine something the size of a cougar. Fuck that π
I've also read that it has something to do with dogs genetics. Their DNA makes it easy to make large changes to their physiology with small genetic changes. That's why there are so many different shapes and sizes of dogs, while almost all cats conform to a similar structure. The cats that hung around us were small and stayed that way, but we went nuts with dogs and made everything from Chihuahuas to Great Danes.
