Because we know Bungie could do better. Some people still hope that Bungie will actually learn from their mistakes and improve the game. Some people critique a game harshly because they love it, but if you keep sucking the game's cock all day long then they're just going to keep giving you the same shit over and over. At this point, they are no longer Bungie the creators of Halo, but Bungie the creators of Destiny and feels like an entirely different company.