Russia probably comprehends that if Israel’s survival depends on defeating this missile, too, that will come to pass. Why get embarassed when your queen of battle comes a cropper before you get to use it on your own behalf? The Russians make a lot of good weapons for low end conflicts, and a few for mid-level, but at the high end they are in a difficult situation. If they sell their top-of-the-line stuff, it might not work as well as they suppose; we might capture some of them or buy them from the same unreliable pricks that that bought it from the Russians in the first place; or the Israelis, or even we, might figure out how to defeat or marginalize it.
And high tech stuff in an air defense equation is enormously dependent on a well-integrated system into which it fits. I would doubt that the Iranians have or can ever develop an air defense system we could not defeat in less than two or three days, with or without Russian help to them (or to us, or both).