it is just bungie trying things to get less players to quit after the first 30-60 days of gameplay if you don't raid the taken king has a pretty short life span as you will fade out when you don't have much use for legendary marks any longer. You will hit the wall somewhere between 290 and 300 ilvl and just give up because your progress is too slow and doesn't feel rewarding any longer. HOWEVER.... if there is a time release exotic quest, some of them may stay or come back to do it read the behind the scenes story at bungie, they don't really have that much content coming so they are constantly trying to think of things to prolong player attention to their game.