When, a couple of years ago at a conference of the American Copy Editors Society, the editors of the Associated Press Stylebook announced that they were dropping the over/more than entry, there was a great wailing and gnashing of teeth and rending of garments.
Editors, I among them, had for years been insisting that over can only refer to spatial relationships and that more than must be used for increases. Attending that conference were Kory Stamper and Peter Sokolowski of Merriam-Webster and Steve Kleinedler of the American Heritage Dictionary, and they were floored to discover a distinction that they had never heard of.
Over/more than, it turns out, is a stricture invented by American newspaper editors in the nineteenth century and faithfully propagated through the industry while the rest of the English-speaking world went blithely along unaware that they were violating a rule when they said "over three years old" or "over three pints of whiskey."
There is a long history in English of people inventing rules to tidy up the language.
Initially, it was because English was a mongrel offspring of Anglo-Saxon and Norman French and a newcomer without the pedigree of French, Italian, Spanish, and German. It needed rules.
So John Dryden and others in the seventeenth century decided that it was improper to end a sentence with a preposition. Latin, an established prestige language, never did that. And preposition literally means "positioned before," people. Never mind that it is native to English.
Then in 1712, in "A Proposal for Correcting, Improving and Ascertaining the English Tongue," Jonathan Swift lobbied the Tory administration of Queen Anne's reign to set up an English Academy to regulate the language and keep out the riffraff. Later, Samuel Johnson thought in proposing his great dictionary that he could fix (two senses, stabilize and repair) the language by establishing the meanings from the work of its best writers—only to concede wanly in the preface to the completed work that language will go its own way, with lexicographers trailing after it.
English spelling is a morass, and many have itched to drain it, but all the proposals to simplify spelling have failed. Noah Webster got us in America to drop the u in colour and the k in critick, but nearly all of his other suggestions were stillborn.
The impulse to invent rules of grammar and usage rises in part from a belief that there is one Proper English that can be enforced, but anyone with any grasp of reality can see that there is no such thing. There are many English dialects, of which standard written English, though prestigious, is merely one, and there are registers within dialects. The combined knuckle-rapping of generations of schoolteachers has failed to eradicate ain't from spoken English, and the double negative thrives in Appalachia and in African-American Vernacular English.
(About that double negative: English ain't algebra. Two negatives do not make a positive. They double down on the negative, and you understand that perfectly well.)
Editors, my tribe, wish to be precise, which is a noble goal, but in pursuit of that goal editors tend to swerve into converting guidelines into Rules—thus the angst at ACES when they were confronted with the blunt truth that one of the Rules on which they had based their professionalism was entirely bogus. (Neither were they happy when AP dropped the prohibition on hopefully as a sentence adverb and gingerly, reluctantly allowed limited use of they as an epicene pronoun. Now Chicago and the AMA Manual of Style are to follow suit. Editors suffer more than they need to.)
Lurking somewhere beneath the surface of the impulse to tidy up the language is social prejudice, an intention to protect the language from the Wrong People—the young, the less formally educated, minority speakers, or simply groups of people we don't like much.
Rules, real and imagined, as I have been arguing tiresomely in these posts, are less important than judgment. Judgment of what works best for the writer, the subject, the occasion, the publication, the audience.
Impact as a verb is much out of favor today (great Fowler's ghost, I won't even bring up impactful), but Katy bar the door is not an effective strategy for editors. Impact might stick, and if it does, resistance to it will come to seem as quaint as the 1940s opposition to contact as a verb. The work of linguists and lexicographers has brought pressure on the style guides to allow singular they, but it is the greater pressure of the great mass of speakers and writers of the language that has established a usage we cannot ignore.