Question

Why power wasted during transmission is less in case of high voltage and low current?

Answer 1

Wire resistance causes losses in electric power transmission. If you keep resistance constant, losses are linearly proportional to voltage but it is proportional to the square of the current. So if you double the voltage, for the same power you have half the current and power dissipation is effectively halved for the same power.

In order to transmit more current and keep losses under control, one would need a bigger wire, with a larger cross-sectional area. Such a wire would weight a lot more than the thinner wire that can transmit lower currents. Heavier cables use more metal which is more expensive, and limit the cable span (the distance between the towers), requiring more towers to be transmitted over the same distance.