I dunno if this is due to the update as I can't blame without any empirical evidences but I did noticed that activity was going downhill after the 12/10 update. What are we to do, how can we revive the joy and activity of our clan? We're a family clan, so we're friends and we mostly recruits friends...
You have the bonus of the clan being comprised of friends and family so you can ask them directly.
Sometimes they just have other priorities in life. You could also find out whether the direction of the clan/game gone off to one where they aren't having as much fun/enjoyment.
Did you try telling them that this is now the perfect game? If they are truly Real Chiefs, they would agree and adapt. Then SC could just go on perma-vacation and not have to listen to the unwashed non-whales.