You would be correct. I have surmised that some years back. It is more than evident without an investigation of spg origins that the bulk of the diving population is hitting 50yo (and not many beyond 65 who are still active divers) and that the years around 1972 was a demarcation line in the beach sand. However it was not the spg that made diving possible for the masses, it was instead the BC. No longer did the diver need to be able to swim and the rest is history, a false idol. Since I came of age in the 70s (60yo) I do not know first hand much of what occurred on the other side of that line, just a bare glimpse and books.
N
Agree completely Nem. But let me add, not only did the BC become the great enabler with regards to fitness, but how about proper weighting? Easy to over weight, (instructors are guilty of propagating this IMO) because the bc will (suspend the overweighted diver like a marionette) compensate for it. This puts the overweighted diver in the perfect posture to peddle like a circus clown on a unicycle.
http://m.youtube.com/watch?v=UfM8BGE3E74&desktop_uri=/watch?v=UfM8BGE3E74
Doesn't do the bottom any favors.