Because they are the worst enemies of the Muslims, according to the Qur’an (5:82). “Saudi Mujahid Sheikh: Jihad Against The Cursed Jews Everywhere Is A Supreme Duty,” from MEMRI, November 23 (thanks to Lachlan):
On November 16, 2012, the “Global Jihad” website (aljahad.com/vb) posted a fatwa by the Saudi mujahid sheikh Nasser bin Hamad Al-Fahd mandating jihad against the Jews. Al-Fahd has been incarcerated in Saudi Arabia since 2003 for praising the Riyadh bombings in May of that year. In 2004, the Saudi media reported that he had recanted his jihadi ideology, but subsequently he published a communiqué stating that he had been forced to do this and that he did not regret anything he had done before his arrest.[i]
In response to the question whether it is permissible to kill Jews and harm their interests everywhere, even outside Palestine, and whether this counts as jihad, the sheikh replied that the Jews are the leaders of the infidels and the greatest enemies of Islam and the Muslims in the present age. Therefore, jihad against Jews everywhere is “one of the most important duties and greatest virtues,” and any guarantees of protection granted them by tyrannical and infidel governments are meaningless, especially when the Jews are attacking Muslims as they please. Al-Fahd stressed that, when jihad against Jews outside of Palestine is more harmful than beneficial, Islam does not permit it; however, the only ones who can determine whether this is the case are the mujahideen, not “those who shirk jihad.”…