Law enforcement has enormous discretion for probable cause and can give straight up contradictory reasons for different cases, it is what officers are taught to do (i.e. something like driving too fast, driving too slow, driving too rigidly at the speed limit). This allows individual bias to overwhelm any attempt at equal enforcement. It's pretty well documented in both The New Jim Crow and Usual Cruelty, the Supreme Court has made it difficult to gather data in the last couple decades.