Two weeks after the leaders of several big tech companies agreed to testify before a Congressional hearing on competition, one CEO—Apple's Tim Cook—was still resisting.  

There was a simple reason for his holdout. According to people familiar with his thinking, Cook was firm in his belief that Apple didn't belong with a group of companies increasingly viewed as antitrust malefactors by lawmakers and regulators, including Amazon, Facebook and Google. What’s more, Cook had spent much of the last four years mostly avoiding the kind of toxic political environment that has engulfed the CEOs of those companies over everything from privacy to censorship to treatment of workers.