[II2II]

It may come down to cost, but other physical properties enter the picture. For example: thermal expansion is an issue for overhead power lines, along with how ductile it is.

In other cases it is more important to reduce resistance, not so much because of the power loss but because of what the power loss means: the generation of heat that may be difficult to remove.

Of course you can get around those problems at extra cost, but it is more than a straight up comparison of the material cost of the conductor.