Maybe they don't trust the US to keep it safe. That's not a dig at US, just the risk assessment any vendor has to deal with.

After recent stories on the F-35, maybe not entirely without reason.

Iron Dome is a guided SAM against (unguided) munitions for kill by kinetic hit or close proximity explosion. A ground radar track hostile munitions, fly the missile into its face to kill like a bullet actually hitting another midair.

So they wouldn't like designers of its adversaries to know how to fly shells to avoid it.

I don't think the US would benefit much from understanding iron dome, as you can likely beat the 14% success rate of Qassam with ramjets, multiple angles of attack, or more than 20 missiles... Not much of a stretch for the US.