The biggest difference is that it takes about 60 minutes of riding to get out of town and into a more natural environment. Those 60 minutes can feel even longer as this time is usually spent traveling on very busy, automobile-dominated roadways, which I find rather stressful.
Don’t get me wrong, There are plenty of bike lanes and routes criss-crossing Tucson, but most of these routes (as mentioned above) do not inspire my style of carefree and joyous riding. It may be a surprise to some, but I’m not an ideological cyclist. I don’t fight against conditions be it weather, road surface, or personal safety just to prove that bicycling is a viable form of transit (although I respect those who do). I ride a bicycle simply because of its potential to enhance the quality of my everyday life.
In other words: I ride a bicycle out of an Epicurean desire for happiness.
Now there are always exceptions. Sometimes I ride for physical exercise. Sometimes I ride to accomplish a goal (e.g. to reach the top of the mountain, or to get from point A to point B within X amount of time). But for the most part bicycling is a way to enhance my own pleasure by drawing me closer to my surroundings and helping me feel the aliveness of my own body.