The reason is because it was an international flight arriving on to a domestic gate. So the passengers cannot disembark through 1L and in to the terminal They must be bussed to an international drop off point in order to go through immigration.
The air bridge will be attached to door 1L for the following departure. And as the steps can’t be put on to the front of the aircraft due to lack of space as the air bridge is in the way, it has to be steps at door 2L.
Not ideal for those in club, but unfortunately it’s the only way! It’s a fairly rare occurrence, but does happen, especially during the busy summer schedule.
Hopefully this explination is helpful!