Because we've never seen him not on the super sayian warriors

Would he be able to be the #1 guy on a contender? No.

Is he a perfect 3rd option? Yes.

He's like Lamar Odom with DPOY-level defense and a killer instinct. Game 7 vs the Cavs showed me he can step up and be THE DUDE when he needs to (though also maybe that was in reaction to being suspended G6). Anyway, I'd rank him in the top 30 easily (current, not all time obviously). But he's an interesting case.