The why of diving is different for everyone. It also changes over time. When I started, I recall it was to add another skill/experience, try something new. Some macho element as it had a "dangerous" label and as a 20 something guy this is/was attractive. That wore off quickly and I found that the work and discomfort (read cold) involved not worth the return compared to all the other demands on my time.
Went diving as a holiday lark and something to do on vacation for years. Kind of like visiting ruins - interesting, fun but not the focus of the trip. However each trip I found myself making sure there was water nearby and the quality of the diving entered more and more into the decision re where to go. Danger didn't enter into the equation at all. This was just an interesting world to explore.
Now I go on diving vacations - whole purpose is to dive. I dive in very cold murky water with way too much weight on my back for any sane person. Macho - don't think so, but I can't spend 2 3 weeks sitting around on the beach, I go stir crazy, and I enjoy explorying this world in my backyard.
I see new divers going the same route. Taking up the sport because it is a "dangerous" activity. They tend to be the ones that don't keep it up, as it really isn't that dangerous. I too have wondered if some migrate to the tech specialties to keep up the adrenaline rush. I can't see any other reason to go to 300 feet for 10 minutes and then spend hours hanging on a deco line staring at featureless pea soup freezing half to death. But I haven't tried it either so until then I reserve judgement.
Re women in diving, there is a real imbalance - this is a male dominated sport in terms of numbers. (Too bad, I like women

) Two things come to mind as the reason. First and most important, women by and large don't do dangerous things just because they are dangerous, they tend to need a better reason. They don't have the "macho" reason to try it out like I did. So they don't try it for one reason and learn to like it for another. Secondly, the gear, up here anyway the gear to dive weighs just as much for a woman as it does for a man. Tanks, suits, lead don't come, by and large, in small easy to carry sizes. Women have to pack just as much gear as we do and that is an impediment to many. My partner (at 4' 11") takes one look at the tank and weight belt and laughs. Won't even try, and I don't blame her. Yes a smaller tank would help, but not that much.
Tech diving may be a similar selection process. Those who go that route start looking for that kick and end up staying for another reason altogether. Just musing here, I don't think Catherine was out of line for speculating that there is a "boys club" macho thing driving tech diving. She may be wrong for many, but I suspect there is something to it for more. No value judgement here, testosterone drives a lot of us to do allot of things we wouldn't do otherwise.
On another front, knew briefly a female cardiac surgeon - she was married to a colleague. The money was great, but I got the impression that the driving force was as described. She did because she could - this was a woman driven by the possible. How far could she go, what was possible for her to accomplish. One of the most self confident people I ever met. I got the sense that she felt that she could do whatever she set her mind to, and for whatever reason needed to test herself at the edge of that confidence.