Because robots shaped for their environment are old news, to the point that most of them aren't even called robots. If you want to wow people and have them feel

Because robots shaped for their environment are old news, to the point that most of them aren't even called robots. If you want to wow people and have them feel a connection to your robot you have to make it at least resemble a mammal. Even better if it resembles a human. There's also the other argument about humanoid robots doing better in environments adapted to humans. But that's so far that hasn't really panned out.