Earlier quoted context omitted.
> teaching 5 year olds the butterfly and other high energy/low safety strokes without teaching elementary backstroke, breaststroke, sidestroke. I am amazed at how few of my early millennial peers have never heard of the elementary backstroke.
I was never taught that and I am older than that and used to swim competitively. I never seen anyone swim that. Likely, it was never standard think to teach.
I suspect that it was never taught for competition, partly because of its energy efficiency through low performance.
I also wonder if it's more common around lakes and oceans; as it's great for going over waves with minimum energy.