Three branches of government. Two chambers of Congress.
All have completely different functions, hence the different ways of choosing people to perform the roles.
And here we are, talking about fundamentally changing the form of government yet again.
What the ignorant fail to understand are the dependencies, the delicate and complex nature of the system the founders designed. They may not have understood it themselves.
When one starts monkeying with a complex system, it behooves one to very carefully consider the implications and impacts of the change on the system as a whole and the other parts therein.
Of course that rarely happens when one is blinded by the will to power.
Very dangerous doings.