@ronbot interesting conclusions. I was searching Greece off season and this is what I found.
Just about everyone agrees that the best time to visit is Greece is spring and early summer (mid-Apr to mid-June) or autumn (Sept to mid-Oct). This way, you'll avoid the summer high season, with its inflated prices, hordes of tourists and high temperatures (heat waves of 100°F/+40C are routine).
Maybe they are sick of the tourists and opt out