It was mostly Bob Arum's fault but, ultimately, Mayweather said it himself that he does not want to fight Pac after Pac demolished Cotto as he was afraid for his health. There's a video to this and you can see it in You Tube. Just search for it. Pac and Roach was really interested in having this fight. Now that Bob Arum is also very interested to make this fight happen, the fault would be with Mayweather if this does not happen.