Can someone please explain why high voltage not high amperag

Solution

We use high power lines to transmit electricity due to following advantages:

1.Reduced Line current for a given amount of power

For the same amount of power to transfer , the line current will reduce and so does the current carrying capacity of conductors. The reduced current capacity will result in the less volume of conductor for a given length.
Contrary to Distribution systems, there are no legal restrictions on voltage regulation in case of transmission of bulk power ,the only criteria to transmit power is the economy of conductors.

2.Reduced I^2R Loss

With the reduction in line current comes the reduction in I^2R loss.

3.Better Efficiency

With lesser Line losses due to reduced I^2*R loss , the efficiency of transmission increases.

4,Improved Voltage Regulation

With the decreased Line current the voltage drop across line will decrease and this will improve the voltage regulation as the receiving end voltage will be more.
Voltage regulation is defined as( (Vs-Vr)/Vs)

5.Better Efficiency due to improved voltage regulation

Regressing back to transmission efficiency , since the voltages are high the power transfer will increase which is substantiated by the fact
P=Vs*Vr*sin (delta) /Xs