Iran is Shi’ite and SA is Sunni. Religiously they don’t like each other at all. We’ll no doubt find that most of the Islamic world will quietly support anything that Israel does to Iran, even if they bluster a little up front. And from a political standpoint, SA sees Iran as a threat to their dominence in the region. They don’t want Iran any more powerful than it already is, so they’ll gladly let “the West” take care of their problem and be labelled bad guys for it rather than themselves. Plus when it comes right down to it, I don’t think SA has the military might to do much on their own.
Too bad Iraq and Iran didn’t just destroy each other, while the world watched and munched popcorn, when they were at war. Would have save us billions.