Question: why do people develop accents depending on where they live?

Dimitar Shterionov answered on 14 Nov 2018:

Nice question. To be honest, I am not very familiar with the details because they involve quite some biology – it has to do with muscle memory and other types of body development from our earliest age. But here is something that I know and read:
Apparently there are two types of accents – a foreign accent and a native accent.
The first type occurs because different languages use different sounds and the body learns how to pronounce sounds that are common for the mother tongue and then finds it difficult to adapt to pronouncing the foreign sounds. For example, in Bulgarian (this is my mother tongue) we don’t have a sound for the English letter combination ‘th’ so often Bulgarians pronounce the word ‘the’ as ‘de’ or ‘there’ as ‘dere’. Simply our muscles in the mouth, the tongue and the other organs have not developed to pronounce these sounds.
The other type of accent depends is the native — when people in a group speak the same language as a larger group but with some differences. Typically this occurs due to social factors – e.g., if there is a high mountain between two tribes that speak the same language, with time on the one side of the mountain people will start using slightly different sounds and words than the people on the other.