Here are a few of the Reasons to Ride I try to explain in my book The Cyclist's Manifesto:

Fun. The simple physical sensation of gliding and swooping around on two wheels.

Adventure. More adventurous than driving to the same destination. Life is too short not to add adventure to mundane daily commutes.

Efficiency. The most efficient form of transportation ever invented. (Bicyclists can easily achieve the rough equivalent of 1000 mpg.)

Exercise. Provides exercise while providing efficient transportation at the same time. Get where you need to go and be fitter/stronger/better by the time you get there, rather than a bit closer to death as you would be after sitting in a car.

Still, bicycling isn't for everybody, and that's okay.