I agree. It's just the culture to be active, fashionable, etc. In SoCal or most parts of Florida, it's just not as socially acceptable to be obese, dishevled, alcoholic, chain smoker, etc as it is in some other places. That also means some arrogant or self absorbed people, but overall, south Florida is just pretty healthy and active. You see a lot more gyms, aerobics studios, health food stores/restaurants, etc here than you do in some many other areas of the country. Even old, retired people are outside walking, playing golf, etc.
It's just common sense to take care of your body when it's beach season 8+ months per year, and everyone else around you is staying in shape. The fashion/modeling/club industry is also pretty big down here, so I'm sure that plays a role as well.