高壓電纜為何一般都是高架而不在地底

An overhead powerline is an electric power transmission line suspended by towers or poles. Since most of the insulation is provided by air, overhead powerlines are generally the lowest-cost method of transmission for large quantities of electric power.
Electric power transmission is one process in the transmitting of electricity to consumers. The term refers to the bulk transfer of electrical power from place to place. Typically, power transmission is between the power plant and a substation near a populated area. This is distinct from electricity distribution, which is concerned with the delivery from the substation to the consumers. Due to the large amount of power involved, transmission normally takes place at high voltage (110 kV or above). Electricity is usually transmitted over long distance through overhead power transmission lines . Underground power transmission is used only in densely populated areas (such as large cities) because of the high cost of installation and maintenance.
AC power transmission is the transmission of electric power by alternating current. Usually transmission lines use three phase AC current. In electric railways, single phase AC current is sometimes used in a railway electrification system. In urban areas, trains may be powered by DC at 600 volts or so.
Today, transmission-level voltages are usually considered to be 110 kV and above. Lower voltages such as 66 kV and 33 kV are usually considered sub-transmission voltages but are occasionally used on long lines with light loads. Voltages less than 33 kV are usually used for distribution. Voltages above 230 kV are considered extra high voltage and require different designs compared to equipment used at lower voltages. Overhead transmission lines are not insulated, so design of these lines requires minimum clearances to be observed to maintain safety.
Electrical power is invariably partially lost during transmission. This applies to short distances such as between components on a printed circuit board as well as to cross country high voltage lines. Loss power is proportional to the resistance of the wire and the square of the current.
Ploss = RI2
Because of this relationship, it is favourable to transmit energy with voltages as high as possible. This reduces the current and thus the power lost during transmission.

地面的電位為零，而高壓電一般為數千，甚至過萬伏特，形成極大電位差，架空可以解決洩電形成電擊短路，損毀設施。 不過，由於架空，嚴重影響風光，及要抵受風吹雨打，所以不少高壓電纜，都已經地下，甚至跨越海底，成本高，但勝在耐用。

嗯，學科上的解釋？
我就只是知道，用架空電纜來傳電是因為成本，
你想下，如果在地底，你要傳到很遠的地方，，
掘地要出幾多錢呢？
有山路，有石路，
掘一掘石路你都要唔小錢了！
這樣算唔算解釋得好科學？