It's risky because if they do it, they have to consistently be as good or better than TSMC, year after year. Makes more sense than trying to build a car though.
They only have to be "good enough" with some wins, Apple was able to survive the mediocre Intel performance and likely could survive some mediocre iPhone chip performance.
But they won't do it unless they need to, or they think they can get a major win, and even then likely though a subsidiary.
