There are two main reasons: one is to facilitate table use. The table should be put dishes, rice bowls, chopsticks, spoons, temporary mobile phones, hats, gloves and other things, and then put a socket is quite obstructed, cleaning the table is not convenient and sanitary.
The other is security. If the socket is placed on the table, there is always soup and porridge for dinner, and it is not only difficult to clean up, but also easy to string electricity safety accidents. For these two reasons, the outlet should be placed under the table.