Well, he wasn't *too* overlooked, since he just re-signed at $13 million per year.
What do you like about him? He's got a long injury history, has barely cracked double digits scoring lately, and the last three years he's shot 33.9%, 33.3%, and 34.0% from 3PT. He's been below .500 eFG% each of those seasons. He's below average at rebounding and passing, and his defense has been really spotty.
He's a shooter who struggles to shoot, and a scorer who struggles to score. He's not worth the taxpayer MLE, let alone double that.