I'm a PP ASEL and I can't say why I got into diving, it's just something I've always wanted to do. The same thing goes for flying, I just wanted to do it, no real reason. I'll be doing my openwater soon enough and based on my aviation experiences I'd say the flying complements diving nicely. For example the emergency procedures, navigation, yearly equipment checkups, ongoing training and a structured environment very similar to flying. It's pretty similar to diving except for the buddy system which we don't have in small GA planes. I tend to relate diving to flying when the instructor is teaching, that way when we cover the checks I'll relate it to a preflight and what's necessary for safety before launching. I kind of treat the instructor as an ATC controller and find it helps out, except I don't repeat back stuff unless asked to. I wonder if we could reword IMSAFE and CIGARS for diving? Actually IMSAFE works. For non pilots here it is, see how similar it is?
I - Illness - Do I have an illness or any symptoms of an illness?
M - Medication - Have I been taking prescription or over-the-counter drugs?
S - Stress - Am I under psychological pressure from the job? Worried about financial matters, health problems or family discord?
A - Alcohol - Have I been drinking within eight hours? Within 24 hours?
F - Fatigue - Am I tired and not adequately rested?
E - Eating - Am I adequately nourished?
Because I'm a pilot I tend to think about what can happen and how to solve problems more so now than I would have in the past. Reflecting on my river swimming days when I was much younger I think I'm lucky all I ever got into was leaches... I had no plans other than to get wet that day, not too bright. Age might also help out here because I now know I'm not immortal and wish to get older.
For what it's worth, at the flyin's I attend I've started asking other pilots if they dive and I get a surprising number that say yes, and I've found many of the medivac pilots are also rescue divers.