Building codes evolve to address changes in how structures are constructed. EIFS, for example, were largely unknown in the United States until the early 1980s. Once the systems achieved broad acceptance, language was placed into model codes to address EIFS materials and application methods.
The need to add language to model codes is obvious; the desire to remove language is less apparent. Blame human nature for the latter approach. When faced with an option to remove language (or throw away something we don’t need) the concept that “someone somewhere might want to do it the old way/ I might need it in the future” generally seems to make us reluctant to boot out the old. Even to our detriment.