Tenure and the reactions of faculty peers can be a significant part of the problem, according to the CHE (in an artcle unfortunately behind a firewall):
Even a professor who is the subject of regular misconduct complaints often cannot be easily removed from a campus. Tenure protects many professors from quick dismissal. Their faculty peers, who are often charged with assessing whether an accused colleague bears responsibility, may view the cases as attacks on tenure. College leaders, who often don’t have the power to terminate a professor without consulting the faculty, may fear damage to their institution’s reputation. Students who experience harassment may not file complaints if they feel they have little chance of being taken seriously.
Nor, as the last sentence suggests, is the victim usually keen to file charges. As Mr Isicoff, the lawyer defending the University in the McGinn case, is quoted as saying, “you’re walking in with the odds largely stacked against you,” as a student.
Part of the solution may consist in steps taken before hiring, as the philosopher Heidi Lockwood said.
…Ms. Lockwood sees it. She said colleges can take clear steps to improve how they handle claims of misbehavior by professors. She recommended, among other changes, that colleges conduct harassment-specific background checks before hiring professors.
Added: I’ve just noticed that the article is utterly silent about the role – or lack of roles – for bystanders. I’m unhappy that I didn’t notice this right away and think we might put some effort into reminding ourselves we should be thinking of taking action. In the Macy case, for example, the situation was well known to a lot of people before formal complaints were made.