Writing in AAVE is silly, just like someone from the Deep South including southern drawl in their writing would be, or someone from Boston spelling “car keys” as “kha kees”

So

African Americans have a weak bias against writing in African American English -> Colleges have weak bias against accepting African Americans as graduate students

Is a bit of a jump. Someone writing in AAVE probably wouldn’t get accepted to college, because written word is supposed to transcend dialects and follow a set of rules to be universally understandable.