Mercurius
Legend
I've never been one to use published settings (half the fun I get from D&D is making my own) but is the basic premise of the OP correct? There are only many settings published for 4E so far but the "settings per year" doesn't seem that out of whack to me. Is 4E really light on new settings?
Well they haven't published any truly new settings in years, but in terms of "new" as in "new to 4E", then the rate itself isn't lower than previously, I think. We've had the FR in 2008, Eberron in 2009, Dark Sun in 2010, and Neverwinter in 2011, not to mention the Shadowfell and possibly Nentir Vale coming up as well. The only one of those that could be considered "new" is Nentir Vale, and the gazetteer has either been postponed or canceled; I suppose Shadowfell could be considered new in that I don't think Gloomwrought has been detailed before.
But my point is less about the number of different settings that WotC is publishing and more about A) the number of setting sourcebooks being published, and B) the number of D&D-related settings as a whole, including other publishers. Other than PDFs, the only non-WotC 4E setting that I can think of is Amethyst, which is science fantasy, and of course Golarion which is the new big kitchen sink setting. But if you go back to the 3.x days, you had WotC supporting two major settings, the Forgotten Realms and Eberron, with new supplements coming out a few times a year for each, as well as various other "mini-setting" books like Ghostwalk. In the 90s you had half a dozen settings that they supported to various degrees. Now they take a "three and out" approach.
Stepping back to the big picture, I'd really like to know the paper RPG demographics and whether any let-up in settings is more due to fewer gamers than new systems.
You and everyone else! I honestly don't understand why a serious, professional demographic study hasn't been done. I'm sure WotC has done their own but if they have, they aren't sharing (at least not since the "Dancey Report" of 11 years ago). All we know is that there many more D&D players in the 80s than there are now and that D&D reached a low-point in the late 90s, resurged with 3E in the early 2000s, and is probably a bit lower now.