Pure incompetence. You cannot outsource your army or national security.
Honestly, the UAE is very vulnerable when it comes to an actual war. If the Houthies really want to hurt them and they decide to accept the potential consequences of it (international outcry and more bombing), they can cause the Emirates hundreds of billion dollars of economic damage with really cheap attacks, costing them less than 100 million dollars in total. It's a war that the UAE cannot afford. And the Emirates lacks the size and the strategic depth of Saudi Arabia. So, things are going to look pretty bad and costly for them if things escalate further than this.