>>508026203 (OP)Hezbollah had shown it was pretty useless, mainly because of Iron Dome. Syria's only value to Iran was as a supply route for Hezbollah, so if Hezbollah was useless then Assad was also useless.
Iran had already wasted over 30 billion dollars propping up Assad. For that amount of money, they could've bought more than 30 thousand ballistic missiles. Iran is running on a shoestring budget; they weren't going to waste additional billions on that black hole.
At least, that is my theory.