Yes, that's why.
I guess that's why people near the Thames changed their accents from other people in London; the little known Great War of the River Thames of 1972. Second only to the 27 Day War of Ontario that took place near the Great Lakes where Canadians universally decided to change their accents from their American cousins despite still revering the Queen.
All positively true.
Accents are 100% voluntary and 100% a conscious decision after a war. No other explanations possible. And in no way does anyone who states these undeniable and universal facts sound at all stupid. Don't be silly, now.