Death means nothing to them, nor suffering, nor hardship. They believe that the more bloody mayhem, mass murder, and destruction they can create, the sooner their Twelfth Imam Savior will appear. Muslim Pakistan already has nuclear weapons, and other Arab countries are actively seeking them.
For over a century things have not been going well for Muslims, and it turns out that they have an ancient and rock-solid belief in their own version of the Second Coming. They believe the Christian version of Jesus returning is actually the work of Satan; and their own Savior, the Mahdi, will come down from heaven and create paradise on earth. He will battle Judeo-Christians and other 'infidels' , defeat them, and cast all who disagree with him into eternal Hellfire.
This article by Graeme Wood in The Atlantic, a sober and well-respected magazine, spells out the religious motivations behind ISIS and other Muslim extremist groups:
These present-day events were prophesied almost two-thousand-years ago by St. John of Patmos, a 92 year-old prisoner-exile of the Romans. We should celebrate, for we will see things no people of any age have ever seen. The reward for us will be too astonishing to describe.
St. John's prophesies make up the last chapter of the Bible, known as Revelation. It describes the long process God initiates before, during, and after the Day of Judgment, the last acts of God to redeem the souls of the righteous throughout all of history. It's written in a kind of metaphorical code, using many strange and even bizarre images mixed in with familiar ones such as Christ, his Bride, the Saints, and Holy Angels. Satanic monsters, terrible plagues, and mass deaths become routine in Revelation. The goodness of God seems to come into question, so it's a challenge for any religious authority to explain it. However, when we look back at world history since 1900, it isn't so hard to understand.
More than 100 million people died in wars, persecutions, famines, and biological plagues since 1900. Over a billion people were injured, both physically and mentally, from their proximity to these catastrophes. In addition, their descendants, you and me, have been impacted and hurt by what our ancestors experienced. So it's pretty easy to make the case that the Apocalypse and Armageddon - as described in Revelation - have been a part of human life for over a hundred years.
WWI, which began in August 1914, transformed the globe and brought us communism, police states, state-sanctioned mass murder, and high technology. All of which has spawned mass atheism, anti-theism, and their opposites, fanatical religions of the most ruthless kind.
Time is extremely short. Say a prayer. Make it a big prayer.