It's simple really. Many of the year 1 items were the pinnacle of what their class could be. Case in point, Fatebringer and Ghorn. There was no way Bungie could create weapons in their class that could compete. All they needed to do was make items for the new subclasses. Add some new gun and armor designs to give people more choices. If Bungie would have taken this approach the game would have more staying power. After about a month of into TTK they would see where they needed improvement. If the player base was sticking with year 1 gear over the new items then changes could be made. But instead we our current game.