GMs profit comes almost completely from large SUVs and Pickup trucks, which gives the union a lot of power.

Essentially, they are selling pickup trucks and Escalades to Americans with fantastic margins to prop-up their car business (which is unprofitable in the US and only occasionally profitable elsewhere) and to fuel global expansion.

Basically if the UAW stops making pickup trucks and Escalades, GMs cashflow will turn ugly fast. Doesn't matter where the growth is.