I don't think you understand what "businesses leaving the US" means. They usually move their corporate headquarters to avoid taxes. No successful business in their right mind is exiting the US market. Carbon credits and the like are based on sales in a particular market, not corporate domicile.
So where would GM move their sales to? NA and China are the only viable markets and China is even-more heavy-handed with EV mandates.
It's called venting. I'm not suggesting that GM abandon the US market.
But with ridiculous schemes like "carbon credits," any business couldn't be blamed for attempting to find a more sensible, business-friendly place to move headquarters and operations.