I think you guys are missing one key point about the attrition rate. Diving is a pain in the ass for the "average" person. First, it requires effort. It isn't instantaneous gratification. It takes time, planning, effort, and money. Compared to playing my guitar, flying RC model airplanes, or riding my motorcycle diving requires a momentous effort and is a continuous expense.
Unless a person falls in love with diving it is probably something that they won't bother to do. Who wants to spend a half hour or so checking equipment and packing, get up early, drive an hour or two to a "local" dive site, and pay $100 to strap on 50 lbs of gear and jump in a cold ocean for 45 minutes at a time. There is just so many other things you can do for a lot less money, (I'm a total beginner and I've got conservatively $3000 wrapped up in gear and training. Not to mention that for each of my 25 dives over the last year I've spent $100 a pop for fuel, parking, air, and boat rides). I think most of my "peers" feel like for a $100 and a lot less effort they can go out to dinner, get drunk, go to the beach, go surfing, etc.
Couple this with the fact that diving isn't easy. I mean it is easy to strap on the equipment, jump in the ocean and breath but it isn't easy to do well and this takes some of the enjoyment out of it. Does it not? I've managed to get 16 dives in over the last 4 months which is pretty good for average smuck (IMHO) and the other day was the first time that everything went really really well with my buoyancy, breathing, etc. For the first time I didn't crash into anything, had decent ability to hover, blah blah blah. I only put my finger down on the bottom one time to push off. This "control" makes diving much more enjoyable, at least for me. It gets more fun every time I go but when a person is starting out, crashing around, getting headaches / jaw aches from sucking air and gritting their teeth it ain't that much fun. Maybe the first few times the adrenaline overrides this but come 0700 Saturday morning of a persons 8'th dive maybe they just don't feel like dealing with it....
So recap, get up early, take a bunch of time, spend a bunch of money, be uncomfortable, piddle around in the ocean crashing into stuff, oh yeah, I forgot, sharks, box jelly fish, and the kraken are all very real fears that add another level of discomfort.
I dive because I love the ocean and the animals. I'm a some what patient person and I knew / know my experiences are only going to get better with time. I love getting up early for an adventure, I enjoy the repetition and methodology of checking over equipment and packing, I don't drink or go clubbing anymore, I don't have anything in my life financed, I have a dive knife / sword that my son gave me for my birthday to fight off the kraken but without all or most of these qualities / life benefits it is no wonder there is such a high attrition rate.
I'm I to far off?