It's a geographical difference, but it has little to do with the deserts, and more to do with the actual density of where people live, where the US is also among the least dense in the world. Those suburbs with 0.3-0.5 acre lots, roads that need to be everywhere and quite wide, extending every distance, just aren't standard worldwide, and increase bespoke infrastructure costs. In a denser place you need more capacity in the fiber bundle, or larger pipes on a sewer, but that's a much smaller problem than the miles of infra. Go look at a density map by the square km, and compare any American metro to, say, a Spanish metro. You find denser square miles in Spanish towns under 500k than you would in Kansas City, Phoenix, Houston... and that lowers all kinds of infra costs. It's not really the miles of desert, farmland or anything like that.