Lol, classic American exceptionalism.

Iran didn't attack the desalination plants because that would amount to actual warcrimes - and they care about their public perception in the broader community of nations. Unlike, of course, Israel and the USA, who don't mind turning a few schools and hospitals to smithereens.

You might call this "assured non-mutual destruction", and of course it helps that the US is located away from Iran's immediate neighborhood, but destroying the lifelines of the GCC countries would assure an economic collapse globally that the world has never seen before. Imagine something on the lines of oil at $300 a barrel, zero fertilizer, zero semiconductors, zero plastics, the works. And Iran could just as easily turn Israel to glass, with a death by a thousand papercuts (or drones, whatever your flavor). Of course, all of this at a huge cost to itself.