The answer to the why lies in the stated purpose and goals of the Muslim Brotherhood, founded by Hassan al-Banna in 1928 and championed today by groups such as ISIS, Al Qaeda, Taliban, Boko Haram, Hamas, Hizbolla and many more.

From Wikipedia:

The Brotherhood's stated goal is to instill the Qur'an and Sunnah as the "sole reference point for ... ordering the life of the Muslim family, individual, community ... and state."[13] Its mottos include "Believers are but Brothers", "Islam is the Solution", and "Allah is our objective; the Qur'an is the Constitution; the Prophet is our leader; jihad is our way; death for the sake of Allah is our wish."[14][15][16] It is financed by members, who are required to allocate a portion of their income to the movement,[17] and was for many years financed by Saudi Arabia, with whom it shared some enemies and some points of doctrine.[17][18]