They are doing those mini events because they have nothing else to add to the game. Everything went fine while they had all that cut content from the original game to sell to us as DLC's, but now that content is over and they have nothing more to give to players. My belief is that they're not going to add anything substantial to the PvE of Destiny until the release of Destiny 2 in 2017. My best bet is that they'll recycle some old stuff already in the game and throw it at us as something "awesome" and "original". Bungie made way too many mistakes managing Destiny, the excessive focus and resources spent with PvP was the worst one (still is), and now it's just too late to make it right. Destiny PvE is decaying to a full stop and I'm not seeing Bungie worried with that. That's why when Destiny 2 comes out maybe it's better to wait some time to see where it goes.