A combination of what everyone has said. The motication with regards to money,the fact that they fought for their legacies rather than purely for $$$. Then other factors such as training for more rounds,fighting more often. Also,every fight used to be a war and they used to beat the shit out of each other. We get excited when we see Corrales v Castillo 1,whcih was amazing but those guys used to carry out wars on that scale all the time!