It's been discussed for decades that the US would run out of precision munitions in any multi-week conflict. The presumption was that the US would either be in a nuclear war at that point, or a ground campaign would complete the task along with dumb munitions.

That the US decided to expend it's precision weapon stockpile on a conflict of choice with no ground or dumb bombing campaign to fallback on is a mystery for later generations. It is not unbelievable that Iran is capable of blocking a dumb bombing campaign indefinitely, or that the viable targets for such a campaign are politically untenable.