I think you are mistaken. There is much to learn from implementations such as this, and the techniques used form the basis of much more complex systems. The technology remains very relevant.

FWIW, I didn't downvote you, as I don't downvote someone simply because I believe they're wrong, or because I disagree with them.

While I agree that it's not just historical interest - there's still much that can be learned from Lisp - this implementation is certainly not the place to learn it. There's no garbage collection, which is really the biggest concern of a proper lisp implementation in a language like C. Without GC, it's a gimmick implementation. There's no practical use for it.

There is much to be learned from incomplete, toy implementations. Not least, the interested reader can see if they can extend the existing implementation to include the missing features.

Insisting that learners/students should only ever read and study complete, perfect implementations is, I think, a mistake. I've learned a great deal from studying, and subsequently improving and extending, implementations that are imperfect and incomplete.