Because Islam isn't really a religion, it is a reproduction strategy that is predicated on low-value males going out to conquer other lands or killing themselves in martyrdom. You are allowed to have up to four wives, not including concubines. In shitty desert wastelands, like the middle east, women will obviously flow towards the men with the most resources. This leaves a large amount of pissed off male incels with no $$$, no women, and no hottie 2D anime waifu! What to do with surplus male population? Make them go off to distant lands, fuck white women who want to piss of their fathers. Or, better yet, promise lots of sweet young pussy in heaven to those who commit holy jihad against the infidels. Then they blow themselves up. More poon 4 u.