This is all real interesting. The question remains why more people aren't taking up scuba. Maybe it's because nobody can even agree on what should be required to scuba dive. Thousands of gear combinations, hundreds of places to dive with all kinds of conditions. As it is with all the discussions here on Scubaboard, there is no absolute answer to the question. Hell, you guys just spent a couple of hundred posts on what level of swimming skills one should have.
I just spent a week in Bonaire, striking up conversations with as many divers as possible. For most of these conversations I pretended I was a non-diver and asked the divers "why should I take up diving?"
I didn't get much of anything beyond "it's so cool... you'll love it."
People who love the sport can't adequately express why someone else should take it up. And there are not "hundreds of places to dive" but rather TENS OF THOUSANDS of places to dive - when you add up every shop, boat, resort, guide, instructor, etc... and they all have their own spin on the "why you should become a diver" story. So there's no consistent, compelling message hitting non-divers.
That is the reason. It's fairly simple.
It's not "the reason that EVERYONE isn't taking up diving" which would be a ridiculous goal. But a clear, compelling message would certainly go a long way towards getting "more" people to take up diving.
And to close the door on swimming skills... there are 319,000,000 people in the US. If we assume that 1/3rd have even rudimentary swim skills that's one-hundred million people with sufficient swim skills to become divers. Once all of THEM are certified we can look at addressing "lack of swim skills" as a reason there aren't more divers.