[Someone]

Looking at https://en.m.wikipedia.org/wiki/Synchronous_grid_of_Continen... and combining that with your remark, I would guess the electricity market isn't "pretty global". Yes, you can ship coal and oil about everywhere, but there seem to be economies of scale in larger networks, especially if your grid spans time zones (people switch on their stuff at different times in GMT), and Europe's does that.

Of the four you mention, three aren't connected to that grid, and I would guess the link with Spain doesn't have sufficient capacity to even out peaks and troughs in Spanish demand (http://ses.jrc.ec.europa.eu/power-system-modelling does show a fairly thin line between France and Spain, both large countries in population)

The above is 100% educated GUESS. Corrections welcome.