Logically speaking they couldn't do it till now. Last gen held back a lot of the game wether people want to admit it or not. Not to mention the taken king essentially fixed a lot of what was wrong with the game. Similar how to Division's 1.4 update aims to fix the base game. Of course i'm not forgiving bungie for everything or stating they are perfect. But saying "it should have been there year 1" isn't productive or really even a decent stance to take.