they're not the same same religion. Christianity can (if you allow self identification) be considered to include both Mormons and Roman Catholics. Those two do not consider one another legitimate coreligionists.
Iran is mostly a Shia state, most of the others are various flavors of Sunni. They represent deep, irreconcilable differences, so Islam isn't really the point on which those states agree. Think Ulster's protestants and Catholics.
The middle east generally could only unite around common interests and common threats, and those threats/interests have overwhelm political ideas like "it hurts us, but it hurts them more, so we'll stand down and let it happen."
