There are millions or billions of quadrupeds surviving on 3 legs every day. 4 legs is evolutionarily superior to 3 but 3 gets the job done, especially if you don't have to worry about agility or repair.

How many animals have wheels? And yet wheels are a pretty practical choice for a lot of things.

Ah, so it’s impossible to make a robot unless it looks like an animal

This one right here

Kangooroos?