They should have said it before going to war...

I’m sure they did. No evidence to suggest there was an intelligence failure, afaik. The failures are, on the evidence, entirely at the, shall we say, executive level.

They did, they even published publicly.

Analysis have been consistent for years: Iran can close the strait of Hormuz indefinitely with minimal effort.

Shippers and their insurers are extremely risk averse. A single dude with a shoulder mounted rocket anywhere in on the coastline is enough to keep ships out.