I care. I had fun racing other guilds. I really like this game a lot and I'll have fun with it regardless.
Pride might be at stake. We've made a name for ourselves on our server and I do sorta like knowing that our guild is in the top 10 in the US.
If we get accepted and maintain or improve our ranking, it will feel somewhat hollow to me. If we don't get accepted and our ranking goes down, I'll feel somewhat cheated.
In the end, you are right it is a game and I enjoy, but competition just adds to it.