At this scale and volume, it's not really about good faith.
Changing fabs is non-trivial. If they pushed Apple to a point where they had to find an alternative (which is another story) and Apple did switch, they would have to work extra hard to get them back in the future. Apple wouldn't want to invest twice in changing back and forth.
On the other hand, TSMC knows that changing fabs is not really an option and Apple doesn't want to do it anyway, so they have leverage to squeeze.
At this level, everyone knows it's just business and it comes down to optimizing long-term risk/reward for each party.
Changing fabs is non-trivial. If they pushed Apple to a point where they had to find an alternative (which is another story) and Apple did switch, they would have to work extra hard to get them back in the future. Apple wouldn't want to invest twice in changing back and forth.
On the other hand, TSMC knows that changing fabs is not really an option and Apple doesn't want to do it anyway, so they have leverage to squeeze.
At this level, everyone knows it's just business and it comes down to optimizing long-term risk/reward for each party.