It should get better.
He's still pretty young. Players often have down years in their career for a variety of reasons. Randomness (my new favorite word) can play a factor, some sort of nagging injury, maybe he was getting exploited on something that he can fix, etc.
Unfortunately he doesn't look like the Hall of Famer that we were all hoping for but he can still be an All-Star caliber player (a real one not a fake one like he was this year) moving forward.