>>479106
I don't think it's really the reason though, it's more social stratification than anything. Due to the fact that for the longest time poorer people lacked any real resources to leave the place they grew up on and as a result you only really ever lived around people of the same social class as you (the peasants certainly never lived right next to the aristocracy), then it's natural that different accents developed that were much more local in nature. People with means can move if need be, they don't need to be tied down to one town until the day they die, so as a result those that do will have their accents change over time.
That being said, the UK aristocratic accent is fake. And I don't mean it's fake as in "fake and gay", I mean it literally sprung up out of nothing. That posh way of talking was invented in the 19th century as a way of distinguishing themselves as the people who got money the old fashioned way (by inheriting it) rather than be someone that's noveau riche and thus can have a lot of money and power but not be an aristocrat.