TSMC is already a major Apple partner, Apple had no reason to start a talent war here. Remember, Apple squeezes suppliers and labor (wage fixing from the Steve Jobs days).
They only build their own stuff when they see a competitive advantage to doing so — when IBM stopped delivering on chip efficiency or when Intel’s chips started stagnating.
TSMC is known to be very selective with cadres. People who are given "keys to the kingdom" are selected among all things upon loyalty. Take a look on their number of GMs, and VPs with 10+ years of work at TSMC. At the highest levels, TSMC kind of stops being a company, and starts looking like a fraternity.
They have the money and can attract the talent