Elon doesn't bring huge amounts of time to his companies, he brings some sort of skill which I don't know how to characterize but empirically must exist given the level of repeatable success he's had.
If there was a job description to "throw this football 50 yards into a trash can, a couple of times per week" I wouldn't be able to do the job at all, but an NFL quarterback might be able to do the job for 5 different companies while also Tweeting 50 times a day.