Frankly, I don't think it's part of their design goals, and I just don't see the market for it.
Further, I really don't see the need. Maybe it's just me, but I'm comfortable in pretty much any edition of D&D with a couple sessions of warmup and a good players to help scrape the rust off. So I tend to play whatever setting I'm in the mood for in whatever edition I think has the most interesting version of it. But I play established settings VERY rarely. Ravenloft is about it when I think of "settings I'd like to run in the future" that I've played or run in the past. And I still have to convert a lot of that out of 2nd into 3rd, which isn't terribly difficult, just time consuming. I also don't "convert forward" running campaigns as many people here seem to do.
Beyond that, I've never honestly enjoyed any of the published settings. They're either "generic fantasy", "generic whacko fantasy" or "generic gritty fantasy" (which is really why Ravenloft is the only one that I give a loop about). I liked thematic elements from Dark Sun, but I'm not a huge post-apocalyptica fan enough to really get into it.
Worse I think, is the division. Everyone wants a different setting to get support. I want more Ravenloft support, someone else wants Eberron, someone else wants Dark Sun, another Greyhawk, etc.... and everyone wants these BIG comprehensive books that convert all the old material (decades of it in some cases) forward and that really just isn't marketable or even very realistic.
Honestly I think their "Guidebooks to ...." model for WOTC's MTG worlds is probably what people should expect in terms of support and probably all we're going to get.