Mendes replaced Jose Aldo, due to injury, in the main event against Conor McGregor.
White now tells UFC Tonight that Aldo was fit but decided not to fight.
"He was medically cleared, but he decided to not fight," White told hosts Kenny Florian and Daniel Cormier.
"He stood to make a lot of money in this fight. The bigger issue was making the weight. You lose a fighter like Jose Aldo and put Mendes in and we added to the gate.
"This fight is breaking every record, pre-buys on PPV, traffic on the website; it's bigger than UFC 100. This will be the biggest fight ever," he added.