Its the infrequent leisure pax. The airlines keep telling them they have to check in really early and expect big delays.

Similar happens with the early morning trans-tasman flights (NZ->Oz). Immigration and the bank where you pay departure tax both only open at 4:30am (for flights around 6am) - but there are huge queues from about 4am. Why? Because the airlines say you should check in more than 2 hours before departure.