Exactly. What have we to gain when both sides hate the US and want to wipe Israel off the map. When your enemies fight each other the best thing to do is to let them go at it.
Actually, it is best to ensure both sides remain at a stalemate and extend the conflict while building support for a secular, pro-US goverment in the wings, covertly of course. Since the Russians and Chinese appear to be helping the government side the path forward is obvious..