Running jiggles me and that's not something I like to do to myself. Also I like the low impact aspects of cycling coupled with the "speed" and distance I get from my expended effort. So I can get all the benefits of a cardio workout with less physical wear and tear when I ride. Furthermore, cycling is my hobby. I like to build and maintain my bike which can be slightly more involved than puzzling over the most aerodynamic shoelaces I should use to give me the .0000000000000000000001 second boost.