From the linked article, this particularly stands out: Among the features identified as more common in legal documents, one stood out as making the texts harde

From the linked article, this particularly stands out: Among the features identified as more common in legal documents, one stood out as making the texts harder to read: long definitions inserted in the middle of sentences. [..] “For some reason, legal texts are filled with these center-embedded structures,” Gibson says. “In normal language production, it’s not natural to either write like that or to speak like that.” - notice how there's a definition right in the middle of the article, and not at the beginning. Anyhow, there is a specific reason for having a definition not in chapter 1, article 1 (definitions) but somewhere down in article 15; lexical scope. That definition is not meant to be used in article 8 or 64, where the same word or phrase may be interpreted "as normal" (that is, still as a legal term, but not the one from article 5). This research seems to ignore that there are different styles of legal texts; you'll find that the civil code of any country is usually written in a different (more modern) style than the ancient "thou shalt not kill" bits of the penal code. Even if new crimes are added, those will be written in the same ye olde style, rather than an updated one (with definitions in chapter 1). Also, legal texts dealing with finance tend to be written in a different style from legal texts pertaining to consumer protection.