That is the characteristic of American culture. Just for show. Where does sound fit in? Generic speech, or even particular accents, are designed to complete the picture. It is sort of like the musical accompaniment of the merry-go-round.
So, where did the innovation come from? Immigrants who were not restrained by the cultural strictures. And that includes women who escaped the male dominion. White male supremacists are right to fear extinction. They are a developmental dead end.