The Bulls with Rose, Noah, Deng, plus cap room for LeBron and Wade or Bosh would have seemed to make a great deal of sense.
Assuming he does not end up there, I would guess either the bad reputation of Bulls management (everyone associated with the 1990s dynasty seems to hate the franchise now) or the idea of always being in MJs shadow turned LeBron off.
I think the way they treated Scotty after MJ left gives them that entirely deserved bad rep. Money is money, though, and I think the big market endorsements have an influence, too. Don’t count us out yet, the Bulls might sweeten the pot.