Important factor is that AC at given nominal voltage V swings between 1.41V and -1.41V, so it requires let's say 40% better/thicker insulation than the equivalent V volts DC line. This is OK for overhead lines (just space the wires more) but is a pain for buried or undersea transmission lines; for that reason, they tend to use DC nowadays.

BTW, megavolt DC DC converters are a sign to behold: https://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jp...