I think it's really as simple as Ali having seen his shots coming, wheras not Fraziers. Foreman really loaded up on everything in those days, didn't use his jab and half of everything powerful came from waist level, which played right into his hands against a bob and weave infighter like Frazier. Ali's tactics and mindgames combined with the crowd being so in favour of him only caused George to become more predictable. I think what's more shocking is how Foreman got rid of Frazier so easily, although it does make sense when you break down the styles.