Cost is the main driver here. I am lefty, but I agree the unions are a little out of control. I am sorry, but a guy who stands in a production line building cars should not be making $125k per year (source was a series on TV, think 60 minutes where they talked to some of those workers).
I am glad unions are there to help make sure people are not overworked and have benefits, but come on guys. You shot yourself in the foot there.