Believe it or not, the UK is not the entire world.

In the US, we have vast stretches of highway with nothing in sight. You can pretty easily find yourself many miles away from the nearest town and with no cell service to call for help. If you get a flat in the middle of the actual desert we have, you're absolutely fucked without a spare. Your options are to wait and hope someone else drives by to offer help or just start walking. Maybe you'll find a gas station before you run out of water. Even in the more densely developed areas of the country you can find yourself stranded a long way between towns. It's happened to me twice before and it's not at all an uncommon story.