People seem to enjoy watching Usain Bolt run, and he certainly doesn't seem to be struggling. Not to mention that he's much less fast compared to the average person compared with climbers.
I think part of that is the time involved. Watching Bolt takes 10 seconds -- the entire event can be shown on the evening news. Not as many people sit and watch the 10,000 meters and even less an entire marathon. The more time involved, the more likely it that you are a fan of the sport/activity.