We don't expect scientists to restrict their terminologies within their own fields to terms with which laypeople are familiar, equally so for those of us in computer science and engineering, so why expect it of another field?
The high priesthood preserved Latin, it's true, concealing the true nature of the religion from the tongue of its faithful parishioners in order to maintain unearned control; this is not the case for Law English as lawyers and judges have nothing to gain by maintaining their own manner of speaking since their pronouncements and judges do need to be explained, in plain English, to the involved parties and the public who have no need of the knowledge of legal minutiae. These 'translations' are relatively easily scrutinised even by non-professionals and a public that is increasingly literate in the law.
That this meaning is unknown to people outside the profession is not necessarily an issue. It is the job of a good legal professional to make sure we never need know whilst they sort the minutiae between themselves.