I think the court’s logic was that a suspect’s knowledge of his rights can’t be assumed by the police, he must be told. That said, I believe British police (or at least they do in very old movies) have been warning suspects of their rights for a long time.
Our constitution was written for an informed populace. It was never intended to protect people from themselves, that is what the Democrats believe. And seriously, at this point who doesn’t know the words, “You have the right to remain silent...”