I don't know that it's all that complicated. Most Muslims have darker skin than you or I and the central thesis of cultural leftists is that oppression of dark-skinned people and women explains history and inequalities. (With the "Asian exception," of course, which has proven most inconvenient to their thesis.) Cultural leftists are more or less compelled to take this stance given this sacrament of their religion. This is why you don't generally find Jews mentioned alongside other groups on their list.