In 2015, when Jack Dorsey rejoined Twitter as its interim chief executive, he raved about the app with quasi-religious fervour, calling it “the closest thing we have to a global consciousness”. But on Monday, Dorsey left the pulpit. He resigned, saying in an email to Twitter employees that he believed the company should “stand on its own, free of its founder’s influence or direction”. But there’s something else going on with Dorsey and some of his fellow tech moguls. They seem to be getting bored and restless with their jobs, and they’re striking out in search of...