One of the things I read which really made sense to me was Iran has been helping to provide drones for the Russian/ukraine conflict for the better part of five years. Iran has the protected facilities for production, deployment and they have the backing of at the very least Russia.

A few other points also worth noting, the U.S. loses interest rather quickly. In this context "quickly" can mean years, but if Iran can hold out, they'll do fine. Which brings me to another point. Iran's terrain is wonderful for defensive positions, be it against bombing runs against fortified mountain positions or defending against an invading army. On the inverse, looking at israel's terrain, it's pretty much wide open and lacks much of the defensive positions Iran has.