So “grammar” moved on. But although scientific analysis clarified organic elements of English grammar, they did nothing to change the more subjective qualities of “eloquence,” which had been by then sitting on three centuries of following Latin’s example.

That’s why we have these non-rule “rules” about things like terminal prepositions or split infinitives. They are engrained in our sense of aesthetic choices, which are choices for style and usage. They are not mandated by grammar.