They have to tow the airplanes over too. Most ex-Mexico AS metal inbound to LAX continues up to PDX, SEA or YVR. But they must park at TBIT first for diembarkation, then get a tow over to T3 to board the continuation. As a lot of this goes on in the late afternoon/early evening when TBIT is really hopping and there's a lot of heavies pushing back, it's no wonder AS/T3 is such a scheduling mess... and if the northbound loads are light, why, what a coincidence -- random cancellations due to "mechanicals" start popping up.