Yes, they come with a bunch of built-in useful stuff, but sometimes you want to add a keybinding to do some editing task you do a lot in a particular project or company, even if it's not useful in a more general-purpose setting.
Don't know what IDE you used but Netbeans is very customisable and extensible.
I think this is true for IntelliJ and eclipse as well and it would surprise me if it wasn't for Visual Studio.
(In fact I think I have seen vim modes for all of these and even embedded vim in eclipse.)
I think I probably didn't explain my meaning well. For Netbeans, Intellij, Eclipse, VS, etc. you tend to have to create a new project to write a plugin.
In Emacs, adding a simple extension is simply a matter of adding a function to your .emacs file. So adding useful functionality is very low friction, low enough that you can afford to do it when it wouldn't be worth the effort in an IDE.
Don't know what IDE you used but Netbeans is very customisable and extensible.
I think this is true for IntelliJ and eclipse as well and it would surprise me if it wasn't for Visual Studio.
(In fact I think I have seen vim modes for all of these and even embedded vim in eclipse.)