Great Vowel Shift
Plague or the Black Death, fast-tracked the levels of migration in England, with the capital and South England as the final destinations. The explanation for this choice of destination of migration might be that despite the infection being present everywhere throughout England, the death rates differed - with the southern part of England as the area with the lowest levels of casualties. The reason behind this is that this area had been majorly inhabited by the royals and the aristocracy, which meant better hygienic conditions and higher levels of health care - essentially presenting better chances to resist, counter and overcome the plague. Furthermore, the surplus of inhabitants in the capital might have fuelled the urge in the original inhabitants to differentiate themselves from and place themselves above the migrants culturally and socially, through a “more advanced” pronunciation of vowels.