All languages are spoken with several different accents. There is nothing unusual about English. And not everyone who comes from the same place speaks the same: in any place there is a variety of accents.
Language changes over time. We get new words, there are grammatical changes, and accents change over time. If you listen to recordings made by people from your own language community 100 years ago, you will hear for yourself that even over that time accents have changed.
Factors effecting variation of accents
There has been a linguistic theory in history, largely advanced by Australian historian Gordon Childe (1892-1957) in the 1930's that climate has influenced human history a great deal accounting for the rises and falls of many civilizations including Egypt, Rome, monastic Ireland and the Pueblos and Mayans.
People living in cold countries tend to speak with narrow/tight lips so that they are not affected by extreme cool weather resulting specific accent which is peculiar when used by a person from tropical climate and vice versa.
The languages and the accents of people from tropical countries are more open and rich in phonetics. There are scientific evidences that the height from sea level also plays a role in variation of accents.
In all sorts of ways, we behave like those we mix with. We are members of social groups, and within our social group we like to behave in similar ways and show that we belong. We do this in language as well as in other ways (e.g. what we wear, what we eat).
People may start speaking in a certain manner because they want to distance themselves from other social groups. Perhaps the best and most famous example of this is the Great Vowel Shift (and a somewhat parallel phenomenon of this in Dutch), which according to some theories might have at least partly resulted from a tendency among the upper classes to distinguish themselves from the lower social groups by their pronouncing vowels with a higher tongue position. Afterwards, this deliberate or half-deliberate change might have been adopted by the lower classes as a tool of upward mobility, and therefore it became more general than originally intended (and, incidentally, messed up the fairly consistent relationship between speech and spelling characteristic to the Middle English period).
Accents as remains of past
If you think for example 200 years or more ago, there were no communication aids like radio or telephone; no-one travelled much unless they really needed to, and so there were many variations in language. In the same country people from one village or town or tribe, could possibly live their whole lives and never visit the adjoining town. Different expressions developed and wide variations in slang existed across a whole country.
Is there a Standard English accent?
There is not a single correct accent of English. There is no neutral accent of English. All speakers of English need to cope with many different aspects and learn how to understand them. Some accents are associated with social groups who have high prestige/esteem (the kinds of accents spoken by so called higher social classes, for example), but there are also many of these ‘high class’ accents, all of them regionally based. The accents that are traditionally taught to non-native speakers of English are high prestige accents from various places.
You should try to speak neutrally about different accents, and not suggest that one accent is better than another. The reference varieties are not 'Standard Accents', because no one is required to use them: compare this to spelling -- we are expected to use the Standard Spelling and do our best to correct mistakes. The reference varieties are not more 'careful' or more 'correct' than other accents -- it's just an accident of history that their speakers were the ones with power.
For some people, use of English is prestige and a sword than a another tool for information and communication. They put extra effort to artificially gain the accent of the Englishmen. Due to geological and climate factors our lips are wide open, so these muppots artificially keep their lips close together and try to mimic Englishmen's (who are conditioned in cold climate) accent even when they communicate with own natives. It is simply a mockery.
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