[mythealias]

It might be he is burned out with all the politics surrounding the claim of his work but not with the work in general. People who enjoy doing something rarely get burned out doing it lifelong.

From the newyorker article linked by deuill:

    The prospect of being awarded a Fields Medal had forced 
    him to make a complete break with his profession. “As
     long as I was not conspicuous, I had a choice,” Perelman 
    explained. “Either to make some ugly thing”—a fuss about 
   the math community’s lack of integrity—“or, if I didn’t do
     this kind of thing, to be treated as a pet. Now, when I 
    become a very conspicuous person, I cannot stay a pet and 
    say nothing. That is why I had to quit.” We asked 
    Perelman whether, by refusing the Fields and withdrawing 
    from his profession, he was eliminating any possibility 
    of influencing the discipline. “I am not a politician!” 
    he replied, angrily.

http://www.newyorker.com/magazine/2006/08/28/manifold-destin...