They aren't supposed to be designed to survive in the wilderness. They are artificial. Also, as fun as multiplayer sounds, it's difficult to program.
The creator of this game is a furry, and a fusion between human and animal is just scientifically impossible, and it'd honestly just look a little grotesque if it were realistic; I believe that the main character being cute and not physically adapted to the environment adds to the experience, because it makes you more attached to your lil fluffball.
Even a hybrid between humanity's closest alive relative is hypothetical; yes, there were likely hybrids between Neanderthals and Humans, but we don't know for sure, and even then, they were EXTREMELY close species; something like a fox or a rat just isn't viable the as chromosomes are too different.