It's not that, it's just that the accents in Britain and America diverged, with some of the most major changes being English becoming non-rhotic in a lot of England (this also carried over to America in some New England accents and AAVE)
There's nothing inherently "posh" about Southern English accents, it's just that Americans often perceive Brits as posh for historical reasons
Isn't the developer of Omarchy a right-wing conspiracy theorist?