Perhaps management shares some of the blame, but so do fellow officers who know who the "bad ones" are and remain silent or cover for them.
Of course, you're right. But if the right kind of management exists, those fellow officers wouldn't be afraid to report a bad officer. In many cases, officers (1) know that their current supervisors were as bad as the bad officers they'd like to report, and (2) if they get a reputation, or are even suspected, of telling on fellow officers, they fear that they'll have no backup or assistance if it's ever needed.
I've seen supervisors, and even police chiefs, who are afraid to take appropriate action because it might hurt their reputation with some officers.
I have a terrible memory for authors' names but there was one book written in which the author said that a police chief has 3 groups he has to try to please, satisfy, or get along with: (1) the city manager, mayor, city council or whoever hires and/or fires the police chief, (2) the officers on the department, and (3) the news media. That author claimed a police chief could survive in the job as long as he had 2 of the 3 on his side, but that if it ever occurs that 2 of the 3 are after him, he'd better be looking for a job. I think that's right.
I suppose everyone wants to be "liked" or popular, to some extent, but I'm afraid too many police chiefs and supervisors try too hard to be liked by officers under their command.