DC is used for some high voltage power transmission, as the peak voltage, for which the insulation has to be designed, is the same as the average voltage. On AC, the peak voltage is 1.4 times as big for the same RMS voltage.
Against that has to be factored the costs of converting the low voltage up to the high voltage for power transmission. Before semiconductors, that would have meant big rotary converters, so using a transformer and keeping the whole lot at AC was easier. Nowadays, it is a lot easier to convert DC voltages, by chopping it up into AC and transforming that. As DC-DC conversion becomes easier, it is done a lot more.
https://en.wikipedia.org/wiki/High-voltage_direct_current