The auto companies fear strikes not only because of increased costs of a successful strike, but also the fear of losing market share to companies not engaged in the strike. The auto companies should do what the Maritime Association did back in the '50's. They got together and agreed they would all shut down their docks. The total closure forced all stevedores out of a job, resulting in a flood of unemployment claims on the strike fund, which was neither anticipated or planned for by the union. The total dock closure meant no one lost market share because they were all closed and the workers couldn't hold out because, without strike benefits, the workers quickly agreed to settle on less-that-favorable terms.
I don't know why the auto companies don't do something similar.
A huge fraction of America’s automobile factory employees are Free (as in speech) Workers, not beholden to any “union”. Their employers are not likely to do anything that will help the automobile manufacturers who are stuck with union slaves for workers.