Because the cost of failure is death and the crew aren’t going to risk it, and the other cost of failure is a couple hundred million dollars in ship and cargo and the insurance companies aren’t going to risk it either. This is like asking why your DoorDash driver wouldn’t just try to run the police blockade to get you your burrito.
I can't say that I know anything about Iran, but if we were to close our straits off so you couldn't enter the north sea from the baltic sea then our navy would rapidly deploy various different mines that lay on the bottom on the shallower parts and control the shipping lanes with things like suicide drones. I imagine Iran would do something similar, only they've probably been preparing for it a lot more than we have.
The strait isn’t wide enough, Iran can see any ships attempting