I had a thought on this while reading - as one who backs in when there is no "rush" I much prefer it for the ease of pulling out later, should the congestion in the parking lot get worse. However if it's a busy lot, then I just pull in and back out later... no biggie either way for me.
But what might be a "root" cause is an old tradition in Hawaii that has been lost, especially over the past 15 years on the outer islands, and probably 25 years on Oahu ... the "talk story to your friend in the oncoming lane" tradition. This is definitely a tradition that mainlanders absolutely HATE, but was very prevalent on the islands till the increase in traffic. If you saw a buddy coming the other way (remember most folks used to drive 5-10mph under the speed limit around here all the time ... even Maui was that way when I first moved there) you would simply slow down and stop when both drivers windows lined up - talk story for a few minutes or until a couple of cars were waiting behind you, then off you went.
Life was MUCH slower paced, you intentionally took the time to enjoy your drives to and from work and if someone wanted to pull out, you'd stop and let them in ... now-a-days it holds up the traffic, but in days gone bye when there was not near the traffic issues it was just a way of showing a little aloha to other drivers.
Times have changed, but faster than habits, and I wonder if the backing in is a carryover from those days as well.
Just my perspective.
Aloha, Tim