Some reasons:
Totally intimidate all LEO with a long, drawn-out trial that discusses their vulnerabilities for hours/day over months
Provide ready-made programming for network news for months
Destroy the police officer’s life with smears, allegations, what-ifs, memes, hashtags, t-shirts that will live on after the trial is concluded
Allow rioting no matter what the verdict
Enrich a select group of lawyers
Establish precedent to seek damages from municipal police departments
Destroy Constitutional protections for whites in any case involving non-whites.
Not necessarily in that order and not limited to the above.