It also recommends that parallel citations to commonly used print sources be strongly encouraged. The Citation system is equally adaptable to printed and electronic case reports and is thus medium neutral. Document references are sequential by year by court by decision. Lawyers have been doing it their way for over a century. Lawyers and judges know how to use their system.
Paper remains the medium for the origin of documents with legal effect.
Above applies to persistent, static legal information. It gets that way after initial versions are final edited and eventually signed by a judge. Adding numbers thereafter could mess up copyfitting and page breaks. Paper publishing was the durable medium of choice for centuries. Page number referencing was OK as that was all there was.