Because the Iranians blocked the entrances with soil. There are satellite photos showing dump trucks at the entrances and the entrances being covered over.
It was a clever move on the part of Iran, because an invading force would need to bring heavy equipment with them, which isn't going to happen.
Well.. kinda? Makes me wonder about just dropping munitions on the entrance, or even just using conventional explosives.
And yes, I don't know the skill set to validate the thought. However, I have seen beaver dams cleared with dynamite, and there's a wide level of explosives which can be dropped or deployed on foot...
(People saying it would be violent, well sure, but so is dropping bunker busters...)
It was a clever move on the part of Iran, because an invading force would need to bring heavy equipment with them, which isn't going to happen.