It is hard to set any reason for selection of such forms of language  . As you know, several  unrelated factors are conducive to the selection of special norms. I believe that if you read chaos and complexity theory, it will construct new paradigm in your mind to see issues ,which are constructed multidimensionallly ,in a new perspective . With such a view, you will let things happens and follow descriptive view rather a prescriptive one.  All in all, if one considers socialist view regarding language planning in broader sense, it can be inferred this issue should be discussed in politics not anymore in applied linguistics.

      In my own view, Consequently, despite all different purposeful effort in language policy and planning, the role adoption(as you mentioned) and adaption should be considered, which are ,to a greater extent, dependent upon language user in the society .

It's closely related to power and prejudice.

Dear Mr. Darani, to me it seems that the answer of your question lies in the statements you provided with reference to  Cooper (1989) and Blommaert (1996). in addition to me this socio-linguistic phenomenon has its roots in politics of language. these "errors" are merely puffs of air in speech but have been appropriated with certain stereotypes which are further determiners of certain political motifs.

thanks