Well, security is one of the reason, but the other reason is their bandwidth use on their native streams. Some people do have a habit of leaving TV running, even though they aren't watching or recording... like they go to sleep with it like a nightlight. That's ok if bandwidth is cheap, but consider the issue when it's hundreds or thousands using the streams continuously.
Maybe the scheduled maintenance on the 24th will address some of this... it looks like it will affect only native streams, not the relinks or relays.