Dubb

It helps to visualize them in the context of the "grand staff," below: As you can see, there's a sort of "imaginary line" where middle C rests, and this is like the bridge between the two clefs. Bass clef is just a continuation of treble clef going downwards, and vice versa: treble clef is a continuation of bass clef going upwards. Think of them as connected. With that in mind, it wouldn't make sense for the same notes to be on the same lines in each clef.