This is all informal and anecdotal, but I'll try to explain my reasoning/experience. In the mid/early 90s, you weren't really a great programmer unless you used a real text editor, so we would all eventually evolve into using Emacs (or VIM for the more daring). But then in 1997, Visual Studio got support for code completion (in VB), and Java and even C++ eventually followed. These language editors improved productivity for programming in those languages so much that it was hard to be competitive staying on Emacs. So perhaps most (~90%) of the Java/C#/C++ code written today is done with a well supported language aware editor (Eclipse, Visual Studio, JetBrains, ...).
Of course, if you are programming in a dynamic language, or a language with lousy tool support (C), then the language-aware editor doesn't really give you much (no static type system --> no static type feedback). There is a greater chance you are programming in Emacs (or VIM), but then you might not want to bother with the learning curve, or you might want something with a more modern non-ASCII UI, so maybe you are programming in Sublime or TextMate. There is nothing really wrong with this, you can be a great developer and prefer to avoid UX-archaic tooling, especially if you happen to also be a strong designer. There are strong trends away from text-based tools to visual tools, and I have no reason to believe that this isn't at play here.
The emacs community is vocal, and is particularly magnified in my field (systems/PL/PhD-level computer science) and demagnified at my place of employment (Microsoft, though keep in mind MSR has lots of Emacs/VIM users). But look at what the students prefer: they have no patience to learn these weapons from a more civilized time. They'll take whatever is the path of least resistance, and honestly who blames them!? Its not like they are losing much.