The Constitution was created and ratified to pursue the goal of federalism. This meant that the State legislature selection of Senators was presumed to look out for the interests of STATES as states. It was considered to be the equivalent of the House of Lords in Parliament and to have a long-term view of politics. Part of this was to emphasize the REPRESENTATIVE nature of federalism and a check on overly democratic influences on the government.
A senator selected by a legislature would/should have the interests of the state in mind, not being reliant on popular support which does not have the interest of the state as a state in mind.
By having the senators elected directly by the people they became merely longer serving Representatives. It EXPLICITLY reduced the power of states as states and was ratified by the states presumably with that knowledge.
This meant that the states that voted to ratify the 17th did so with the knowledge that it curbed state power as the Constitution as a whole was designed to do. There are many other instances of the states readily giving up their sovereignty.
Thanks for the clarification. I’ll have to take a look at Article I, section 3, of the Constitution which was modified by the 17th amendment, and see the difference.