If you look back on man's achievements, and don't take them for granted, you will better be able to understand, and perhaps answer the Why question yourself. Consider for a moment the art of flight. When the Wright Brothers decided to build an airplane, I think the most often words emitted from the curious spectator would have been "Why in the World"! I could be wrong in my assumption, but it had to have asked at least once. And once was enough to invoke a stream of answers to the curious onlooker, who might, or might not understand.
On the surface, the answer to the question is - Why Not. When I am asked the Why question, it invokes a stream of answers; some based on the excitement of the flight, and some based on the emotion, the expectations, and uncertainties of the journey. It will undoubtedly be the only such flight I take, but I hope it invokes a litany of memories not only for myself, but for those I meet along the way.