The primary purpose of language is understanding. Forking a language to convey some sort of cultural distinction has the unfortunate side effect of making this more difficult.
Languages are learned individually by each child, depending on the environment that includes family, friends, and the whole town. No two kids can have exactly the same upbringing.
So, having multiple dialects is pretty much the natural state of any living, thriving language. To artificially unify them is a conscious choice that needs to be justified.