1) 'Good' diplo players moving to clans and invite-only games.
2) WarLight losing popularity in general.
3) They really get tedious after 20th game with half players booted in turn 3, four PE's, no fun roleplay and general noobiness.
^ Sums it up well.
Open games get too many cancerous players or don't fill at all.
So people who are actually skilled move to invite-only games.
Add it up to problems in WarLight's falling playerbase and there it is.