In my experience most people who back in have experience driving vehicles with restricted rear visbility like cargo or work vans. I know driving those is what did it for me.

My favourite example is driving one of those vans into a self serve car wash. It will be way harder to back out of one than into one because the vans have no rear window and you cannot see past the building. Backing in is much safer and easier in this case and i think it would be reasonable for car wash owners to have signs requesting all customers back in. They can be busy places with pedestrians around.