Apparently IT was needed in the trade for his salary, not his talent.
Initially it appeared that the Cavs made the trade to bolster both a run for a title in 17-18 AND their post-LBJ future. Speculation that IT could keep Lebron in Cleveland or that the pick would be used to pick up a piece for this year's run fueled present and future narratives as well.
Now it appears that IT was filler and an expiring rather than the KI replacement and future glue for LBJ.
Cap room, Nets pick and Zizic (and a low salary starter in Jae) are the return for the 25 yo all-star who needed to be gone. Of course, this theory is contingent upon the IT as damaged goods premise - which none of us know for sure.