The problem is that Bungie decided to make their vaults and menus overly complicated. In doing so, they've made these portions of the game very resource heavy and that limits how much can be rendered by older gen consoles. It's all based on available RAM after the rest of the game has been rendered. New gen consoles can handle it easily with 4gb of RAM but older gens have just 512mb or 1/2 gb of RAM. Since they decided to release the game on both consoles, they have to keep it fair across the board to prevent a serious problem since older gen versions were the same price as newer gens. Basically, they screwed up by making the game too resource heavy and planning on the newer gen consoles.