Why are high voltage power line cables so thin?
High voltage power lines are thin because they are designed to reduce the amount of energy lost as heat due to resistance in the wires.
The thinner the wire, the less resistance there is to the flow of electricity and the less energy is lost as heat.
High voltage power lines are also made of materials that are good conductors of electricity, such as copper and aluminum.
These materials are expensive, so using less of them by making the wires thinner helps keep costs down.