Think he just convinced himself he was untouchable.....the distance from the mid west area he was controlled by (not just Chicago!) that he took advantage of and the complete raising of the bar in violence he encouraged as a result out there led to the upper echelons being left with no choice but to whack him - the cops threatening accarado/aiuppa about Spilotro's behaviour (in relation to the threats against the cop who accidently killed a connected guys son) finally nailed his coffin shut...