I think it's mostly because Seth is more of a PG. He's a pesky defender, but he can't guard bigger SGs. Mismatch from hell...but I suppose he's better than any type of defense Belinelli provides.
Between the 2 Duke products, I seriously believe Seth Curry is better than Austin Rivers. Very under appreciated by the teams he's played for. Is he like his brother? Absolutely not but certainly would be a decent back up.
I was thinking Tyreke Evans might be a potential target. It's tough to trade Collison after the season he's having but he's too good to be a backup PG, Seth should play more, and a combo guard who can score at a similar rate but defend both backcourt positions would make more sense for us.