accents get lost/changed when in isolation or when mixing different accents together
like think of australian accents and how it used to be some sort of british accent. then you have new zealanders who have their own accent from the same source. being on a separate island away from your original homeland causes people to start talking differently. accents usually reinforce each other
like you ever met 2 different people from texas, one that has a stereotypical texan accent and one that just sounds like any other american with the generic american accent? both born and raised in the same area. probably cause one of them pretty much only hung out with other people in texas that had the same accent, and the other probably never developed a texan accent cause he spent most of his free time watching TV or playing stuff online or whatever and was mostly exposed to people that didn't have a texan accent
Yeah, I only got an accent in my 20s as my parents were very adamant that I learned to speak properly. Now I'm able to speak proper Dutch without a hint of an accent or dialect, but I'm also able to quite adequately mimic dialects and accents from around the country. People have no idea which region I'm from if I feel like it