Could just be that Kayvon Beykpour got replaced by someone better at the job?

Baseball fans know of Wally Pipp, who was a solid first baseman for the Yankees for a decade or so. One day Pipp had a headache and was replaced in the lineup by a young Lou Gehrig, who turned out to be one of the greatest hitters in baseball history.

I have no idea if Jay Sullivan is a Lou Gehrig talent, but he's been doing the job while Beykpour is on paternity leave. If you're the CEO of Twitter and you believe the temp guy is doing a better job, why not make the change?