When the Burning Legion started their invasion, the Alliance and the Horde were some of the first responders, leading to the disaster at Broken Shore.
Afterwards, some of the leaders appeared throughout the Broken Isles where it fit. Genn and Sylvanas had their thing in Stormheim, Tyrande and Malfurion in Val'sharah, Anduin showed up later together with Genn at Broken Shore to visit the spot where his father died.
However, we're now at probably the most important battle in this war, the invasion of Argus. And the leaders of the Alliance and the Horde are nowhere to be seen. Velen is there, sure, but more as a delegate to the Army of the Light than a leader of the Alliance.
So what are they all doing at the moment? What's Sylvanas doing? What's Genn doing? What's Anduin doing? If I recall there's also a trio of dwarves somewhere we haven't heard about in forever. Baine has pretty much gotten zero love for ages. Same with Lor'themar.
I mean I know I shouldn't expect much since Blizzard has always been terrible at equally dividing the spotlight between faction leaders, but still.