Strangely, it's the insular dialects across Britain that have become more bastardised over time. The North American English dialects are far more conservative when it comes to evolution. As this BBC article[1] says: "[...] although there are plenty of variations, modern American pronunciation is generally more akin to at least the 18th-Century British kind than modern British pronunciation. Shakespearean English, this isn’t. But the English of Samuel Johnson and Daniel Defoe? We’re getting a bit warmer."
[1] https://www.bbc.co.uk/culture/article/20180207-how-americans...