Ok so first thing, my understanding is the industrial production of interceptors is done in annual batches, since the final assembly of the missile is the culmination of several long processes and supply chains. It takes something like three years to manufacture an interceptor from complete scratch. They're not just computers strapped to a bomb, think of them more like simple supersonic jet fighters, including many of the same parts and tolerances for aircraft and that should suggest how long these things take to make. Second, the American imperialists haven't exactly been precise in their choice of targets. They've been shooting decoys, they've been triple tapping targets, and they've been targeting things of minimal strategic importance like civilian infrastructure (bridges, schools, etc.)

Third, there's an issue in supply chains for semi-conductors right now, which is kind of a global issue in computer parts rather than specifically for weapons.

I think in conclusion this stems from a complete mismatch in predicted industrial capacity and long-standing American military doctrine. America has been sending munitions to Ukkkraine and the Zionist entity for years, and then opens up another front in Iran. The past several decades of American military strategy has been more focused on rapid air-strikes and then occupation style forever wars. I don't think there's been much consideration of combat with an enemy who has a comparable stockpile of munitions. Furthermore Iran deliberately uses a strategy to waste American interceptors using decoy drones and things massive waves of less sophisticated munitions to waste interceptors.

Ok on that last one, here's a way to think about it. Iran will fire a wave of 50 Shahed missiles, each costing around $20,000 ($1 million in total). A single THAAD interceptor costs upwards of $12 million. A patriot interceptor battery with a full compliment can easily cost $1 billion. That should explain some things I hope.

edit: Oh and I also forgot to mention one of the most important parts. The pentagon is currently staffed by drunken foolish pedophiles who are high on their own narcissism and don't want to listen to the advice of the older imperialist ghouls who actually knew how to do empire. So it shouldn't be a surprise that American literally runs out of weaponry.