Why do people speak in different dialects?

Because different pronunciations formed in different sections of the globe. Also, some counties speak more advanced or developed version of a language like how in South Africa they speak 16th century dutch (Afrikaans) because the dutch invaded south Africa in the 6th century and that's all they have known of the language. But in the country of origin of the language Holland it is further developed. I hope this helps! :)

C. the delegated powers