Question for language purists: how do you account for the evolution of English?

No self-respecting linguist would ever trash AAVE or anything other form of language outside of the standard form. If you have met linguists that speak out against it and are only supportive of prescriptive grammar then they are either not true linguists or they are terrible at it and don't deserve to be calling themselves linguists. Linguists love language and love all forms of a language. To a true linguist, the more branches that grow from a single language the more enjoyable it becomes to study.