What's not to understand - the point of the AP system is to provide an incentive to do the same content a thousand times over without making new content. No sarcasm, that's why it exists. They want you to keep grinding the same mobs and instances and they designed a system for that where they just slap a couple of numbers every now and then, players are then supposed to celebrate and have a lot of fun going back to the same mobs they already saw to grind them for another thousand hours.