Not sure if it's the right subreddit... I recently watched various videos of people reading Shakespeare and older English literature with the original pronounciation, and remained astonished at the radical difference of the sounds they used back then respect to these days. As an italian native speaker the surprise was double, as I remember in school reading old italian at literature from the '200/'300, and being able to almost understand everything at first glance. And I heard that also other languages (chinese for what I know) haven't actually changed so much, as the English Language has done. So why did it change so much? Or is it that many other languages changed a lot in these centuries, and the real question would be: why italian (and chinese) hasn't changed that much?
While I don't really have an answer to your question, you might be interested in this older answer of mine on the standardization of Italian language. The intellectual debate about the Italian language has always been moderated by the enormous, and lasting, influence of early Tuscan poetry and literature. In the absence of a single national language, book publishers and authors all over Italy tried to adhere to the "Tuscan Standard," even if it deviated from everyday language or from their own dialect. Although numerous authors (especially non-tuscan ones) came into conflict with other authors (typically tuscan ones) on how closely to adhere to the "old tuscan" literary standard, they nonetheless retained the language of the "tuscan classics" as an important benchmark.