They were sunset on the premise that Bungie could replace our losses. Which they didn't. They couldn't keep up. If you really want to blame anyone at this point. Blame Bungie leadership. The dudes above the Game director. Back to answering the question you had. In short sunsetting done right keeps the hamster wheel healthy while giving you a reason to keep playing and it allows for anything broken to have it's time then fall away. I saw the potential in that idea but then I also saw Bungie's incapability to do it right.