When welterweight Floyd Mayweather was No. 1 on Sports Illustrated’s Fortunate 50 last year—knocking out Tiger Woods, who had been No. 1 every year since SI started producing the list in 2004—it looked like a fluke, the result of the $85 million he received for his fights with Victor Ortiz and Miguel Cotto. Now Mayweather is proving that he belongs at the top. From just two bouts this year, one earlier this month and the other scheduled for September, he will earn at least $90 million, ...