Wondering how we get ergative languages, my thoughts went to a theory of language change I came up with, no doubt spurred by a variety of things I’ve read. What I hear is people hoping to emphasize what they are saying, often simply to get themselves heard. An recent example is the word “literally” where someone will say something utterly ridiculous like “That sun literally burned me to a crisp” when the speaker would be dead if that were a literal statement. But we will never see a reversal of this and eventually we will have to find another word to express “literal” or at least the adverbial form.
It does say something about human relations that we seem to seek ways to make ourselves heard. This notion of emphasis or intensification accounts for items like fronting of objects e.g. It was the pancakes I ate, not the orange, where I could have just said I ate the pancakes, not the orange. Other examples abound. You might try listening for more examples. I believe this might fall under the term “pragmatics”.