I think Chicago had to move Deng in order to bring in another star player.
Keeping Deng, D-Rose and J-Noah together would have cost the Bulls ~$45-48 million a year ... and we all know those three aren't good enough to win a title without a fourth high quality player.
It is not like they have lots of trade opportunities. Deng, in particular, will never be a player that commands high trade value because he has been proven to not be able to lead a team. To be a go-to guy. He is a complementary player. And teams won't give up a king's ransom for guys like that.
So keeping Noah + Rose and positioning the Bulls to become players in free agency is the best way forward for Chicago to add a legitimate third star to their team.
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Which brings me to this question, is Chicago now the front-runner to sign Carmelo Anthony this summer?
A D-Rose + Melo + J.Noah, Big Three, to build around long term. A top defensive center and rebounder alongside two of the very best offensive players in the league. A top defensive head coach in Tom Thibodeau. Plus, maybe they can even keep 1-2 of Taj Gibson and Jimmy Butler to lead supporting cast. A young stretch four in Mirotic to come over. Does anyone have a better offer than that for Carmelo Anthony? I don't think so. I think Chicago has the best offer.
And even if they miss out on Melo, does that make Chicago one of the main destinations for Kevin Love (as a fall-back) 18 months from now? A Big Three of D-Rose + K-Love + J-Noah.
I think so.
That is why they needed to get rid of Deng.