And as the OP said, maybe only once or twice per GW, so you do this only when there's a real opportunity, and not just to mess up with a competitor, or just easily climb the ladder.
Also, there are countries where it makes sense: an old Soviet airline will most likely base in SVO, as it's the only airport opened to the rest of the world, and where you'll have 50% of your fleet. However once the USSR collapses, DME gets bigger than SVO, but you can't relocate.