I'm not gonna go as far to say that Floyd doesn't have part in it because he sales himself as the bad guy and people just love to hate him and wanna see him lose because of his personality, but he is not able to carry a PPV on his own.
He always has another big name to help him (Cotto,Mosely, especially DeLaHoya) If he fights the likes of Guerrero or Alexander the sales will reflect unless he has another name like Canelo or another really attractive fight on the undercard.
His first huge payday was the DeLaHoya fight where Oscar was the bigger draw which is why he dictated the terms and got the bigger share.
If you look back the numbers may look similar from that point, the difference is Oscar could have fought a cab driver and it would sale, and much like Tiger Woods he would bring in the casual fan like only Mike Tyson could do.
The thing alot of people don't take into to consideration, is Floyd also has the advantage of social media that Oscar and Mike never had, to go with the inflation in PPV prices. There was a time ealry in Oscar and Mikes where fights were on close circuit and there was no PPV.
I know this is gonna sound like hate it really isn't, all I'm saying is that Floyd is strategic in the fact that he fights on the 2 biggest Mexiacn holidays of the year taking over Oscar's dates after his career and he has another big name to help. If he fights Alexander he will have to have another name on the undercard or the sales will reflect.