This is a response to the ongoing - and quickening pace - of their military setbacks in Iraq and Syria. Iraqi Army and militias moving swiftly across the Nineveh plain and on towards Mosul, SAA driving through Palymria towards deir ez ezzor - being raced there by the New Syrian Army and the SF/FSA who are step by step encircling Raqqa and cutting off the Iraq and Syria ISIS controlled areas from each other. No new offence launched in nearly a year, unable to defend the areas they still control when placed under pressure, fighters deserting in droves and turning on each other.
This has a tactical aim - and is diferent from most previous suicide bombings in the area they have carried out which were products of ISIS offensives - they had direct military aims i.e were part of a direct attack or were used to panic civilian populations and soften them up before an atack a few weeks or months later, or used to stir up shia/sunni violence. This, though is defensive and exemplary - it's saying despite the military defeats we are still here and we can still reach our enemies, those of you in non ISIS Iraq can too - do as we did (that's the type of thing they have historically aimed at supporters in the west). Rather than the old come to us, come fight for us.
(And yes you're right Gromit, it is an ideal opp for you to attack people who wished to show their sympathy and solidarity to victims of previous attacks that they were more aware of in a manner not to your liking or who don't have your 100% record of public solidarity and sympathy to victims of all attacks everywhere and at all times. I mean your heavy presence across the iraq and syria threads shows this record quite clearly).
