Like many things, the damage was done by the British. Specifically one Bishop Robert Lowth. In 1762, he wrote a book of prescriptivist grammar rules starting with the premise that Latin is a perfect language, and any construction in English that doesn't match Latin is a flaw. This is where those nonsense rules like "never end a sentence with a preposition" and "never split infinitives" come from, as well as the claim that the singular they (in common use at the time) should be phased out in favor of the generic he, because that's what Latin does. The damage this one book did to the English language still has not been fully repaired.