ISIS wanted to recreate the Caliphate, and shocking, violent videos were one of the most effective methods of recruiting young, belligerent, impressionable males. Martyrdom, beheadings, and violent Jihad were things long before ISIS, and they simply put on the mantle.
to put it another way, you only saw the violent propaganda, since it was in the interest of the US Gov, Israel, Turkey, et al, to make sure the world saw how brutal they were. You didn't watch the hundreds of hours of non-violent propaganda or theology, such as the recruiting videos aimed at young Islamic women.
ISIS wanted to recreate the Caliphate, and shocking, violent videos were one of the most effective methods of recruiting young, belligerent, impressionable males. Martyrdom, beheadings, and violent Jihad were things long before ISIS, and they simply put on the mantle.
to put it another way, you only saw the violent propaganda, since it was in the interest of the US Gov, Israel, Turkey, et al, to make sure the world saw how brutal they were. You didn't watch the hundreds of hours of non-violent propaganda or theology, such as the recruiting videos aimed at young Islamic women.