Transmission costs only capital. Opex for transmission is practically free.

And capital isn't free. With physical goods, there is already a number of existing roads, train tracks, and ports.

Capital costs is why Hawaii has traditionally imported oil versus having an undersea power connection to the continental US.

Hawaii has abundant sun and wind, and deep ocean hard by for cheap storage.

When costs are all capex, the more you use, the less it costs. (And, as with nukes, the less you use, the more it costs.)