They mostly believe that the west has grown decadent and weak, and is ripe for the picking. Hell there are video interviews of multiple imams preaching this. While the modern beta nu-male is busy obsessing over things nobody really gives a shit about and buying body pillows because girls need to consent to everything, the amount of alpha Chads in our society diminishes. Mohhamed, however, was rised in an enviroment embodying "comfort is weakness" and "the strongest survive". Therefore he comes over and collects everything the weak men neglected to take care of.