Why do you think no effort was put into improving the Queen's Wrath event? Priorities. That's why. Instead Bungie improved Iron Banner, created the temperate buff, made Light Level matter, added weapon reforging, etc. Their main focus was PvP and they choose to improve it instead of PvE. Just look at how much effort they're dedicating to improve Trials of Osiris. It's not like "flipping a switch" there is complicated data analysis and rebalancing to work on after each event. As for the expansions, they have both PvE and PvP elements. Back in the days of Halo when everyone used to love Bungie DLC used to cost $10 for just 3 maps. No weapons, no campaign content, no armor, just 3 maps. It's not because Bungie isn't capable of providing a PvE quality experience, it's because their main focus is PvP. You can choose to ignore this, but it's like trying to cover the sun with the tip of your finger. It may work for you, but it's still there.