You lost half the player base already, when you decided on using the same maps, no resets, for over a decade. Things don't stay fresh that long, you shouldn't expect them to, and it's evident that things, beginning around 2009-2011, got real tired out. There was suddenly a lack of enthusiasm amongst the player base, with less wars, less realms, less players. This is the most obvious reason for the decline, and it ought to be what you address if you intend on fixing things.
