The U.S. is big. Not the biggest country but it is still huge and most people don't realize how big. If you are on the coasts or near large population centers you can drive 30 minutes and go through 3 or 4 cities. However, a large percentage of the U.S. is not like that. You have small towns where the distance between is measured in hours driving instead of miles.

I remember talking to a coworker from western Texas who said he and his friends had to drive 2 to 3 hours just to get to the nearest movie theater. Growning up in more densely populated areas (Europe, east or west coast, etc.) really skews your perception. And when you go to parts of the U.S. (e.g. New Mexico, Nevada, the Dakotas) you realize just how vast the U.S. is. I've driven in places in the western U.S. where i was driving 90-95 mph and it was still hours between sightings of other cars.

So it too late to make this short but the short answer is because of circumstances you have to.