I’m no expert, but I think this is a matter of international politics. Imagine if Iran had closed the strait last year. I suspect a rather large coalition would have shown up, quite quickly, to do their best to reopen it. But instead almost every relevant player is pissed off at the US and Israel and has no desire to join in the hostilities.

Not to mention that Iran did not want to have thousands of fancy missiles and bombs lobbed at them, but since that happened anyway, why not close the strait?