I think that the chapter and verse quoting is a performance. It's something they do for the benefit of their followers, since it plays to their emotions and gets them pumped up to kill and rape. Also, if you keep your strategy to yourself, instead of telling your flunkies everything, then it doesn't matter if the flunkies get captured, sent to Guantanamo Bay, and waterboarded. They've got nothing of value to say.
I think the real strategy has fuck-all to do with Islam, and everything to do with earthly power. If Satan can quote Scripture to suit his purpose, why shouldn't DAESH leaders do the same with the Quran?