The numbers that you quote fail to persuade people that most cops are good because most people do not believe those numbers.   It only takes a few bad cops - and a few other bad cops covering up for them - for people to think that "every cop is a criminal" (as Mick Jagger once said).

Every cop may not be a criminal but there are far too many criminals among them and all the denials from people trying to defend the cops make that even more believable.