Well, I think lisper nailed it in the article: It's not just that the code is represented as data structured in linked-lists, it's that that data exposes the semantic structure of the code in ways that are more pragmatically useful (among other nice properties) than char strings.

When you get into the LISP interpreter itself, which is just a linked-list structure describing how to process linked-list structures (like itself) as code, well... Here's William Byrd on "The Most Beautiful Program Ever Written" (ye LISP interpreter) https://www.youtube.com/watch?v=OyfBQmvr2Hc