----just maybe it's because those airline crews are concerned about the possibility of unknown VFR traffic in the class E airspace.
What wonderful logic, you stay at low level in G in case there is un-notified VFR (which will have a transponder) in E --- with no idea what is in G, with or without a transponder.
I also love the proposition that "IFR" is automatically "safer" than VFR, regardless of where you are ----- as if G through A is an ascending hierarchy of progressively "safer" airspace, once again only proving that most of you naysayers simply do not understand ICAO based CNS/ATM ---- and have a manic determination to not understand it.
Tootle pip!!
PS: This reminds me of what was going on, in and out of Ballina, during the "Class G" trial --- the original trials of E. How many of you still remember ----- overflying Ballina, letting down in the firing range at Evans Head, and coming back down the coast at low level in G ---- all to avoid the dreaded E.