Vi(m) and Emacs are almost 40 years old. Why are they still the standard, and what attempts have been made at coming up with a new flexible editor? Are there any features which can not be built into vim/emacs?

My question is similar to this one: Time to drop Emacs and vi? No one had a suggestion, which surprises me. I would have thought that the core of a texteditor is very small and that people brew their own. Perhaps nobody wants to deal with supporting all the modes?

Edit to clarify my question: Instead of writing modes and scripts I ask myself, why there is not a much lightweight project, which lets people custom the editor more directly? Vim has 365395 LOC (C lines all included), Emacs 1.5 million LOC. Why is there a project with say 50k LOC, which is the core, why people can use more freely? Perhaps there is such project, I haven't looked very far. I thought about putting together modules from Vim myself and experimenting with some ideas. The core of editing shouldn't be more than 10k? Vim has a lot optimizations which is really an overkill nowadays. Basically I'm looking for a code base for my own editor and Vi/Emacs are I believe not intended to be used in this way.

Bill Joy said the following about vi.

http://web.cecs.pdx.edu/~kirkenda/joy84.html

The fundamental problem with vi is that it doesn't have a mouse and therefore you've got all these commands. In some sense, its backwards from the kind of thing you'd get from a mouse-oriented thing. I think multiple levels of undo would be wonderful, too. But fundamentally, vi is still ed inside. You can't really fool it. Its like one of those pinatas - things that have candy inside but has layer after layer of paper mache on top. It doesn't really have a unified concept. I think if I were going to go back - I wouldn't go back, but start over again.