I proposed exactly such witness voting years ago. I was right then, and you are right now. Guess why it didn't change? Because the whales want to be absolutely in charge of the witnesses. They are the man. The control what code the witnesses run. They control Hive.

When Steem began ~36 whales mined up commanding stakes to control the witnesses. Today ~36 whales have a commanding stake to control the witnesses, and witness voting 30x stake weighting is why.

Thanks!