To me the problem is in how character (and I guess by this I mean gear ) progression is too strict in how they designed it and so there are no rewards out there to make you more powerful or to work towards something.
So even if they came up with massive amounts of content, since it's not designed with the "working towards something" in mind, it'll never last past the first time you do it, we have the evidence of that in Criterion Dungeons.