For instance, why do they all have to shout "Allah wakauba" (God is great in Arabic) before they blow themselves up?
Why do they all read relevant parts of the Koran in their video clips, to justice their acts?
Why does ISIS, Boko Haram, Al Qaeda, Al shaba all have establishing an Islamic state as the main cause of their jihad?
Why do they all call western women "whores", simply for not dressing up like they force their own women to dresstyjgh
The simple answer to this is because of recruitment. Al Qaeda did not start off as being Islamic terrorists. They started off being anti-american terrorists who happened to be Islamic. Their original targets before 9-11 were American military and infrastructure targets (similar types of targets to previous terror groups such as the IRA or ETA). Then Bin Laden noticed that he was getting support from non-arabic muslims world wide they changed their tactics and goals became straight up Islamic terrorists. Others such as Boko Harem followed suit with aims of combatting any western influence. Then you have ISIS who basically just copied all this but cranked it up to 11 and actually became a muslim death cult.