The Eastern Conference wasn't such a mess a few years ago. In LBJ's first year with the Heat the East, while still weak in the middle, was very strong on top. The Celtics were still together and won 56 games, Miami won 58 with the first year of their trio together and Dwight was still on the Magic who won 50+ games for their 4th straight season. And the best regular season team in the East that year? The Bulls with 62 wins the most in the entire NBA. When the Bulls landed Jimmy Butler with the 30th pick in the draft it was with their own selection.
Then they matched (actually slightly bettered) that output the next year- despite losing Rose for 41% of their games. Their record with D-Rose was on par with a 67 win team during a normal season.
This is the context to remember this Bulls team in, the top regular season team and an actual contender in 2012 if Rose hadn't gone down in a playoff game against Philly.
The next clue to why they refuse to trade Deng is the fact that the Bulls are not old *yet*. Dunleavy and Boozer are old and declining but Deng, Gibson and Noah are all 28 and still have prime years left in the league. This puts the Bulls in a very awkward space going forward if they tank as gunning for a high draft pick means that even if they are lucky enough to land a future star his ascent will coincide with the decent of essentially the rest of the team, and to do so also makes it difficult, if not impossible, to upgrade their roster for Rose's return next season. Lets look at some cap numbers.
Without Deng on the books the Bulls are still committed to 64 million- 2 million over the projected salary cap- across only 8 players. With minimum cap holds of 500,000 each they are ~ 5 million over the cap before a potential Boozer amnesty, but they also have their own draft pick + possibly Charlotte's pick (top 10 protected) eating up another 2-8 million in space. Even after dumping Boozer the Bulls would only be opening up a maximum of 12 million in cap space, and more likely something in the 6-8 million range. Ask your self this- how many FAs in that range can replace either Boozer's or Deng's production, let alone both?
The Bulls best bet for contending in the near term is a return of Rose and using Deng's Bird rights to stay over the cap and try to shift out a similar team to the one that led the NBA in wins from 2010-2012. Boozer's decline will be offset by the rise of Butler and Gibson (hopefully).
Isn't this gambling an awful lot on Rose's return? Yes, but that be was placed years ago. Rose has 3.5 years left on a contract that will pay him 21+ million in the final season. If he returns at any thing less than a borderline All-Star level the Bulls will have an Amar'e Stoudemire sized albatross around their neck until the '17/18 season.
Functionally giving up Deng for salary relief only this year means giving up on the next 2-3 years of contention even if Rose returns healthy. The difficulty of adding an near All-Star caliber player when you start the off season several million over the cap is what is preventing a move like this.