I think usually the writers in kids shows can have more fun with evil characters, they are antagonists, they are supposed to be the one you root against. People are not usually supposed to look up to the villains, they look up to the heros. So the heros need to stay safe so that the people looking up to them (especially if they learn moral lessons) can imitate their good actions. Meanwhile the villain usually has NONE of that of that so throw whatever you feel like, no one will care. This gives writers more fun and interesting takes with them. The villain can act big, bold, exaggerated, because you are not going to be a bad guy are you? No, so the bad guy can be whatever is interesting for the heros to stop. This isn't every show mind you and I could totally be talking out my ass but that's the impression that I got with characters like Robotnik in adventures of sonic the hedgehog.