Why don't any countries use 360-volt or higher mains power?
The premise of your statement is incorrect. Industrial and commercial installations routinely use 380-415V (outside of North America) and 480-600V in North America, and that's just looking at what is called "Low Voltage" distribution. 

RESIDENTIAL mains power is deliberately kept at lower values because anything higher requires different (and very expensive) design considerations in order to remain safe enough for unsophisticated users to be interacting with it. Even at 240V and 120V levels, many many people are injured by electrical accidents now. At higher voltages the rate of injury would increase, as well as the severity.