There are no car foundries or car part vendors that Apple can impose one-sided manufacturing or sourcing agreements with.
Uhh, GM, Ford, BMW, etc. already do and have far less cash on hand than Apple does to throw around. There are literally hundreds of parts suppliers in the world that would bend over backwards for Apple money!
GM, Ford et al. are lucky to reach 20% gross margins. Apple would struggle to equal those margins because it can't guarantee volumes similar to the incumbents. Phone suppliers sell their souls to Apple because of the volumes and because there are no viable alternatives. Apple will have neither of those advantages in the auto world.