Partly it's my love of sunshine and having grown up in an age when sunshine was GOOD. (Funny how what was GOOD when we were kids is now bad, while many of the things that were considered BAD are now GOOD. When bad things become good, it's easy to rush towards them, but when good things become bad, we aren't as quick to run away.) Also I believe that exposure is not necessarily exhibitionism (though I must be more of an exhibitionist than your average person or I wouldn't have spent most of my adult life in media.)
Or maybe I'm just afraid that one day a one-piece is all I'll be able to wear in public. And once that line is crossed, there will be no un-crossing.