Because defenses will key on him more. Okafor will need to learn to pass out of the double team this season.
I really think in terms of individual talent Uconn they are far and away the best. But you also need chemistry and health--that is why Zona didn't win last year (clearly the most talent) or in 98 when they had their whole championship team returning, and it is why Duke didn't win Brand's last year or Maryland's year. So many things have to come together chemistry wise--and even if health is good whether Villanueva, Okafor and Gordon are all on the same page versus treating this year as an NBA draft showcase is not a sure thing. Further, often even the most talented and most well oiled teams need a little luck here and there to run the 6 strait or whatever it takes to win it all in the turney.