Why is it Pacquiao's purse against Cotto bigger?

[Maranao]

In Pac-Diaz, Pac got approx. 5 million, Cotto in his latest outing against margo, got only 3 million.

Pac-Diaz was a total mismatch and a flop in box office..

while Cotto-Margo is a VERY HARD fight for cotto ( eventually cotto lost )

so y is it? I thought Cotto is a bigger draw than pac with all Boriquas on his side.

[Zocalo]

Margarito got 1.5... that is why

Diaz only got 800K.

You have to pay your opponent as well...