Blizzard probably tried to make a distinction there. The Alliance epilogue / celebration is a public speech towards its members and citizens (we see Gnomes, Draenei, Pandaren, Humans and Worgens there, there might be probably some tiny Dwarves I missed). Those citizens were happily cheering for the success of Azerothian force's victory on Argus under a nice blue sky, and for the message Anduin just delivered that no one, not even a King (leader), is more important than the Alliance as a whole (which made of mainly citizens / soldiers instead of leaders).
On the other hand, the Horde epilogue is a rather sober, rather-gloomy-air private meeting between the Horde leaders inside a building. We didn't get to see Horde citizens cheering. We didn't see a free sky, nor did we see any smiles or clapping, except for a brief moment after Baine tried to lighten up the mood (and if not for him, the mood wouldn't even be out of place if it was a meeting after we lost). Just all business (and some suspicions) between the bigwigs. Everything just seems rather... contained.
If that's the case, I understand that they are trying to portray two factions with different images and focus. However, personally, I'd preferred if they depicted Horde members as well. Maybe showing a festival at Ogrimmar outside before zooming into a tent / building for the leaders meeting. With the current depictions, it's like they are implying that the Horde is about its leaders, while the Alliance about the members. That doesn't sound too nice for the Horde (and would be a bit unfair for the Horde leaders who truly care for their citizens as well)