It's a bit of a delicate balance for the U.S. (forget Israel, they simply must do what Uncle Sam says). Continue to leave fractured Syria out in the cold and risk that it will fall into the hands of Islamic fundamentalists, or engage it and strengthen the military dictatorship there. The U.S. prefers to deal with military dictatorships above all. However, before forcing its chief enforcer in the region to cough up the Golan, the U.S. wants to make sure Syria will come fully into its sphere of influence. Egypt was in the same boat some decades ago, but it's a much more important country and hence received higher priority.
Yemeni ISIS affiliate claims responsibility for Sanaa mosque bombing (Reuters)