LaTeX and Emacs share a feature, they are both contain a core written in a low level language (For TeX it was Pascal originally, and for Emacs it is C). Anticipating the need for extensions, both systems are open source and include user programmability, a powerful macro based programming language for TeX and a fully integrated Lisp system in Emacs.

This has allowed both to grow in functionality, year after year. Code written by users wanting particular capabilities has led to so many fantastic enhancements. No one user or committee could anticipate the many ways that these programs could be extended. Although, it would be nice if these systems could be cleaned up and modernized, this is only a dream. In practice, nobody has the time to start over on these enormous bodies of work comprising millions of lines of code.

It's too bad, because it's a joy to use ether of these system once you've spent enough time reading their extensive documentation and puttered around with them for a few years, but their eccentricities and anachronisms keep them out of the hands of many users.