Hey Cameron940, please don't fail to acknowledge the fact that these marathon runners, cyclists and triathletes ARE elite athletes. They just don't look the way you think they should
They look this way because of what their bodies need to be able to do in order to excel at the sport.
Gymnasts have a typical physique, swimmers have a typical physique, weightlifters have a typical physique, etc. For the most part, you can pretty much tell what sport a person is into by looking at their physique.
Cyclists are in fantastic aerobic condition, and triathletes are nothing less than amazing in what they can perform (they have to excel in three disciplines, and just think about how tough an Ironman Competition is!). Personally, I think marathon runners are completely insane and look like they've spent too much time in a concentration camp, but if they enjoy what they are doing and think they look great, who am I to say "you look like a walking skeleton?" They are doing what they love to do, and I know I certainly couldn't do what they do.
When I was in track and field, my training was very different from the longer distance runners. I was muscle-packed; they looked like they needed a decent meal. Our bodies looked very different because our disciplines and training methods were different. I thought I looked fantastic. The long distance runners thought they looked fantastic, too
So at the end of the day, I think it just boils down to personal preference and body perception. And also what you like to do "fitness-wise". If I loved to run miles on end, perhaps I'd be more content to have a different looking physique. But I've been hooked on muscle and looked this way for so long, I can't imagine looking any differently. It just wouldn't be "me".