Pretty much summed up here but one thing that was also a contributing factor was that Ali never was able to grab hold of Frazier and absolutely neutralize Frazier. There was a very fair amount of holding but Joe never let himself get smothered like Foreman. Also, Ali was on his feet a lot more against Frazier which surely drained the gas tank. He also ran into a couple shots while moving, which obviously never helps. He squared up a lot to Foreman, more than he ever had before at least. Otherwise, everything everyone mentioned is essentially correct.