Incentive in a game should be: being able to beat some new bit of content because you mastered that which came before it. Incentive is being able to progress further because you as a player actually gained some insight and/or skill. All the arguments people speak of considering the state of the game are true - but the conclusion some or many of these people have drawn is outright wrong - they concluded WoW or the WoW players are to blame for this. They are not. Anet is. And I doubt Anet is looking to create a WoW clone, but I am confident Anet is completely out of options as to how they should create incentive to play without some fundamental changes to this game's core mechanics.
The best incentive to play a video game is to be better than everyone else playing it. Arena Net does not seem to understand this unfortunately.