Here's one good reason: unlike most "IDEs", Emacs has been around and it will stick around. When I started programming, Turbo Pascal was all the rage, I then u

Here's one good reason: unlike most "IDEs", Emacs has been around and it will stick around. When I started programming, Turbo Pascal was all the rage, I then used Borland C/C++ IDEs. I saw various incarnations of Microsoft's Visual Studio come and go, get redone and rewritten. Every microcontroller vendor seems to try to ship their own IDE for some reason. All these IDEs come and go, and your customizations (or extensions) are lost. In that same time, Emacs has stayed, and while it is being actively developed all the time, you can have a single IDE that works over a time span of 25 years or more. Parts of my init.el (Emacs initialization file) are from 1993.