I commute for several reasons

Cost, I got tired of forking over insane amounts of money for a car

Joy, I enjoy riding my bike, I always have... and I find I am a happier person by commuting by bike instead of being locked in San Jose gridlock

Health, I had quit smoking a month prior to commuting full time... I have lost several inches around the waist since

Experience, I have found that by bike... everything looks different... and all in a positive way