Because states are political units. If you don’t like the laws of one state you can move to another, and this extends to the state's voting power when choosing a president.
As to your innovation in voting, if you accept immutable aspects of identity as the basis for voting rights you're opening the door to some terrible ideas, like ethno-states and Jim Crow laws. Again, without embarrassment at the facetiousness, I'm also not sure how actually making the Jews have more power in 1930s Germany would've solved their problems. Would've probably fuelled grievances: "Hey, Adolf, you know that Jews really do run Germany?" Eeek!
The best way to protect minorities is by the protected freedoms of speech and to bear arms, not by weighting votes by arbitrarily chosen characteristics.