I know many people have talked about this over and over, but I will take my stab at this in my own way. Have you ever noticed the imbalance in battle cries? You can probably think of a bunch of them right off the bat and 90% of the them will be Horde ones. When thinking of the Alliance ones you have "For Khaz Modan" and "For Lorderon, For The King". Honestly those were the only 2 I could think of that are used very often a all. One of them in fact applies to a kingdom, which doesn't even exist anymore. Compare this to "Lok'tar Ogar", "For Honor, For The Earthmother", "Here come the Voodoo", "Dark Lady Watch Over Us", "Anar'alah Belore" and these are ones just off the top of my head. There is a huge imbalance.
Now is this because there is much more pride in being part of the Horde. The Horde has had to fight for its place in the world and will keep letting people know it. Every race who is a part of the Horde at one point or another struggled with something. The orcs with the demon curse and having a place in the world. The Tauren with the endless war with centaur and finding a place they could call home. The trolls been in countless wars and never been able to settle before another mishap happens to them. The undead? Do I really need to explain? And, of course, the Blood Elves who had their entire kingdom destroyed, their prince corrupted and having to be slain by their own hands. It is as if we are preaching look what we have been through and where we have come. Bring it on!
Just some food for thought. Enjoy your weekend.