That simplifies it too much. Cost > sales. The unions demanding more was just the final nail.
I only heard it as background noise but it seems some Boeing employees in SC got into a little hot water over talking unionization during work hours. Which, if they had a ******* brain, they'd know the only reason Boeing moved from WA to SC was to get away from union costs. It would be fitting for Boeing to say "**** this", close the SC plant and move their **** to Puerto Rico.