Blame the writers for not being capable of writing how the “monarchy” actually works. As it is now, the Alliance is the alliance of three remaining Human “kingdoms” (Stormwind, Gilneas, Kul Tiras), three Dwarven clans and their subclans, a merged Gnome kingdom, the Draenei, the Night Elves, the remaining High Elves, and the exiled Void Elves.
There’s wouldn’t be much of an alliance if the Stormwind monarch were bullying everyone around, and right now we have plenty of proof that especially Anduin have been working for unity and cooperation - as he changed his father’s plans about how to unite the three dwarven clans in Ironforge during Cataclysm.
My hope is that we get a faction merge ASAP, with the inclusion of a brand new all-race faction that will be villainous and never cooperate with Hordalliance no matter what.