Surprisingly, the "American Experience" bio of George HW Bush does a workman's job of explaining this. But it was really the demise of Nelson Rockefeller that ended the Liberal and Moderate Republican as a thing. After all, he was divorced.

Topologically, the Left pulled farther and faster, and there was also a reaction to that.

Industry became fragmented, and that's much harder to organize into unions. It was different when there were a small number of large monolithic firms.