There are probably plenty of reasons that account for this besides the challenge factor (and it is challenging, especially the first time -- even when you know what to do, having it come together in practice is always a learning experience). But there's also: 1. People buy in, but leave when they find they don't like the game in general. 2. People finish the story and are satisfied. 3. More anticipated games from bigger names come out. 4. People don't like raids. I don't particularly like raids, after the first couple times -- they're as repetitive as everything else in a loot shooter, [i]and[/i] they chew up more of your time. One-or-two-and-done is how I usually treat them. 5. People get frustrated with other aspects of the game, and leave for greener pastures.