If I think about why we wouldn’t the only thing I can think of is that we want them to take out the rest of Iraq and provoke Iran.
Iran would wipe the floor with these guys, but there would be a loss of strength. It might even get a reaction from the Iraqi army.
In the end you have a weakened Iran, “invading” another country. That would be justification for action against them.
Other than that, I cannot think of why no one is taking action.
I think these guys are too smart to provoke Iran. They’ll just glare at each other.