The reason for such extremism from Muslims is both the desire to virtue-signal how devout they are to their fellow morons, (I mean Muslims) and a genuine fear that they might end up in hell if they do not follow the will of Allah. They believe that hell is an eternal abode for those who enter it, and that their suffering will continue forever, (and that folks is a lot of suffering!) It isdescribed in several verses in the Koran, e.g.
[i] They will long to leave the Fire, but never will they leave there from; and theirs will be a lasting torment. (Quran 5:37) [i]