Same thing that happened across the entire nation, it became clear the Dems have no answers for America.
About half the Libertarian vote defected since the Senate was at stake but this was not key.
Additionally the leftists are disgusted and voted Green, and the Republicans probably came out in greater numbers to seize the prize.
Thats my impression.
I think you are pretty close to the truth. I know I am a Libertarian that was so fed up with the dems, and knew how close this thing was that I went out and voted (almost) straight Republican this election. I know alot of fellow Libertarians that did the same.