I think, and I don't know why anyone thought it was a good idea, that clans actually have a maximum number of people who can actively be in the clan. And from what I've heard, it's some insanely small number. Like less than 200 people. Edit: I just looked it up again. It's apparently 150 people. 75 for Xbox and 75 for Playstation. So unless they increase or remove the limit, the only way you can make this your active clan is to wait for someone else to change their active clan to another group. I'm not one hundred percent sure this is true though.