The first feedback I received on the Adventurers' Guide was that player's don't want to read more than one page of setting material. Bundled right along with this revelation was the fact that any DM who writes a setting manual of any kind is suspect, that they are automatically placed into a dangerous category of nutjob who probably won't run a good game. To me, this is bizarre; it led me to think about the way that D&D has changed since I started playing it, which is a topic that seems to get a frequent workout here.
The assumption that home-made D&D settings are somehow inferior to the boxed products seems to underlie that statement. Let's not even begin to try to unpack the sadness of the claim that reading a book is too much work for someone who wants to play a roleplaying game; the inherent contradiction there must rest for another time. But really, it brings home a shock that I've experienced all over the internet: people simply don't like homebrewed material. It looks like D&D has gone from something you make to something you buy, which is a true loss for the community. The same clearly can't be said about the OSR, so there's some hope yet, I suppose.
Roleplaying games always had a very strong streak of DIY when I started playing them. It wasn't uncommon or unheard of to purchase a "book" or "magazine" that looked like it had been photocopied in a library for cents a page. Groups were expected to customize the games, adapt them to their playstyle, and even to design settings for themselves. There really was no implied setting, and being told that you had to use a boxed campaign set was an insult.
While I ran the Forgotten Realms and Planescape from time to time and a friend solely ran Al-Qadim, no one else I know ever ran a long game set in any of TSR's official worlds. Any foray we took into Cerilia or Athas was a brief one, and it would always end sooner or later in favor of a home-brewed setting. They came fast and furious when I was young, but as I grew older there was but a single setting that I found myself working on; fleshing it out, carefully and slowly adding information and that was the 10th Age.
TSR never seemed to be pushing for an elimination of DIY ethic. The books always suggested that you should throw out anything that you didn't like, combine what you wanted with other editions or systems, and generally make a collection of things that would suit your gaming group well. Even after the Big G was forced out, they continued to tow that line, which was classically Gygax's.
Yet, this pervasive attitude to homemade creations (rules, expansions, settings!) flies in the face of the strong DIY atmosphere of the D&D of my youth. I suppose I haven't been involved in the heart of things for too long, since I stopped giving a shit after I played 3e for a year and was disengaged again when I preordered 4e for the sole purpose of utilizing their internet game table only to discover that, upon release, there was no such thing.
Apparently, D&D isn't something you make at home anymore. D&D, and maybe all rpgs, is something that you buy at a store, pre-packaged. When you get home, you open up the can, and out falls your setting, rules, and more, all form-molded to fit inside the can which in this case is a shiny (but often anemically thin) book. I still remember when D&D wasn't about buying the meal, but rather about buying a recipe.