my motiation would be first and most important is that i simply like to pedal, mountain, road, bmx or whatever. The best way ive heard it described is how many times have you driven into work and said, what a great drive...now how many times have you gotten home from a ride and said that it was great
next would be gas is litterally too expensive for me to afford driving 40 miles a day.
other than those would be im working my towards being a stronger endurance racer, i like the fact that the more we reduce the demand for gas, prices have to drop eventually. Helping the environment isnt too bad either (knoxville has TERRIBLE air quality)