It's a product of its time. In the mid 70s when Emacs was originally created, the MIT Lisp Machine Project had already been going for a few years, and Lisp was kind of a big deal at MIT's AI Lab, where it was created. When Stallman started GNU Emacs in '85 or so, he took lots of inspiration from Lisp and those systems.

You can think of Emacs as a kind of software Lisp machine with an emphasis on editing. Although that analogy only works well if you squint or if you don't know a lot about Lisp machines.

As someone who first learned Lisp through Emacs Lisp, I found it fun, well-documented, and powerful. Once you grok the basics of how the system is dynamically glued together, infinitely hackable, and self-documenting it's kind of mind-blowing.