The US intelligence community long ago gamed out all the risks surrounding a conflict with Iran, including the possibility Iran would close the Straits of Hormuz.
If the Trump administration and Hegseth are surprised now, it's because they've never listened to, and sidelined, the experts.

@petergleick

That's pretty much a given.

Trump can't sit still long enough to hear a proper briefing and all Hegseth hears when briefed are reasons he can't swing his you know what around, and since his is the biggest one anyone has (except his boss of course), no one is going to tell him he can't, so he stops listening/asking and does what he wants.

There was never any chance they'd consider how this could quickly go south before pulling the trigger.