They do it in EU prime time because it inconviniances the least users, most of the population (providing its simalar to ffxi) is JP, then NA, the EU. its basic network maintanance you try to cause the least disruption, if the game had regeonal servers they could stagger the maint when people arent playing, but this isnt possible on ffxiv.

They always did this on ffxi as well, and people just got used to it, it will not change.

Oh and @viion 7pm GMT is EU primetime when over winter UK and Portugal is GMT and UK is GMT+1 in summer, This maint just happens to run the whole of EU primetime and 3hrs into NA primetime.