Different national conditions. The United States is a power generation and supply company, with its own power supply and distribution network, small area and no long-distance power supply. Therefore, there is no ultra-high voltage and high voltage (above 300KV) power supply network in the United States.
China is a national power supply network, and the distance from west to east is far, so it is necessary to use high voltage and ultra-high voltage power supply to reduce line loss.