It's not so much that but that they are right next to Iran and their harbors in the UAE are literally right across the water from the Iranian border, making those harbors a sercurity risk to the U.S. and the rest of the world.
By that I mean, there is nothing to stop the Iranians from bribing a cargo-ship captain and dropping off a WMD onto the cargo-ship as it passed by the Iranian coastal border as it was bound for a major U.S. port.
You might think about what UAE folks have at stake here.
Really? Then why haven't they done it?
If terrorists can do something, they will do it, as soon as they can do it.