Why do Turrets do no damage.

People would call this a tank meta. OK thats fine but why are they able to tank turrets and take no damage. riot should really just buff them. some people might say well then the squishy champ then take more damage. Why do we not have the best of both worlds. Make the turrets do damage based on HP%. that way it would damage the tanks and not tickle them and the squishes will not be killed as fast. everyone would die at the same speed. that way your not getting dived by 3 people and they all live with above half hp at level 5.