So then how would you tell other people that you were struck by a car? Would you say you were hit by a "kiwen utala"? "I was hit by a hard object". Okay, does that mean a book fell on your head? Or someone bumped into you?
And if "towo tawa" is a "space used for movement", then how would you distinguish it between any of the other spaces used for movement, like a bus, train, airplane, elevator, shipping container, bobsled...
One of the values of a word like "car" is it can be used to refer to something independently of how it's being used, which is helpful when things can be used in more than 1 way, and you want people to understand you're talking about the same object in each case.