Can anyone explain why the crew trim the rudder instead of the aileron trim to level the wings…
Sub,
Your question can be rephrased in such that the answer becomes clearer.
Why aren’t the wings level? Because when the wings are level the aircraft won’t hold a steady heading.
Rudder trim is therefore required to reduce the yaw rate to zero for the aircraft to hold a steady heading with wings level.
However, it is easier for the pilot to trim the rudder on a steady heading until the wings are level, because it is easier for the pilot to detect small bank angles with zero yaw rate, than it is to detect small yaw rates with zero bank angle.