If the BCS doesn't establish a champion, what is the point of of it?

I always thought that the BCS was established soley to determine the national champion. If it was, then why should there be talk of co-champs. It seems like if it fails at that twice, then there is really no point in it, except for frustrating everyone. Albeit, Georgia's had a fantastic season and USC had a great Rose Bowl win, but they didn't make it to the Championship game. The BCS exists to prevent other claims to the title, if it can't do that, why bother keeping it?