The reason why the states went with popular vote for Senators? Because people were paying way too much attention to statehouse members and the Senators they voted in! The rule of thumb for any legislature is to evade responsibility in order to stay in office. That's why such bodies are happy to pass their powers to somebody else, it helps them hold their comfy seat longer.
The ploy worked. For me, until the Convention of States movement came along, I cared little who my state rep was. They have little say now in how we are actually governed. Power in the District of Corruption is nearly total.