Pinging as requested.
In the meantime, the states had been passing calls for a Constitutional Convention for the purpose of writing its own version of the 17th Amendment. When 32 states had acted, by 1912, the sitting Senators got nervous. A Convention could have provided that all sitting Senators were out in the street to be replaced wholesale.
Notice the final paragraph of the 17th Amendment. It said that the amendment "shall not affect the election or term of any Senator chosen before the Amendment becomes valid...." The number of states who had called for a Convention was enough to trigger a new Convention. Remember we had 47 states then -- Hawaii, Alaska, and Arizona were not yet in the Union.
So, the Senators read the handwriting on the wall, conceded the Amendment, while protecting their jobs until the next election. On paper, the 17th Amendment followed the usual pattern of proposal by Congress followed by ratification by the states. However, the back story shows that this Amendment (which I agree turned out to be a bad idea) succeeded only because of the Convention calls from the states.