I think what's driving the U.S. hesitancy is the ordnance shortage.
Of course, at least partly. But chaos just won't believe it
Crazy that everyone believes the US is suddenly short on ordnance but Eeron seems to have an endless supply. 
Not trying to antagonize you, this is almost always in good humor
US delayed promised deliveries of Patriots to Japan by a couple of years. Pentagon itself says it's because the US needs them in Iran. I could list several other countries who were told the same. Trump said he doesn't want to send the billions worth of weapons to Taiwan. This was a huge lucrative deal but suddenly Trump changes his mind. I think it's very well established by now the US is catastrophically low on ordnance - the precision missiles. US officials say it openly, including Trump.
Many years ago Iran had considered investing in jets. After analyzing what would be the best bet to invest in, they went all out on missiles instead. So they built an industrial complex, much of which was buried under 500 meters of granite rock so conventional weapons can't touch them, all US/Israel can do is bomb the entrances which the Iranians clear within hours or maybe a day or two. Trump JUST said he thinks they have now built back. We don't have cameras inside the underground facilities so we can't
know how much they have. But the US obviously isn't so confident, otherwise it would attack with little fear. The US is afraid of the Iranian missiles, the Gulf states are absolutely terrified.
TL;DR
Iran is probably able to build new missiles underground, we can't know how many missiles they have exactly, obviously. Iran claims they are at 120% of pre-war levels, US intelligence estimates they are at 90%.
