Why Nepal schools need complaint response mechanisms

One of the news reports that really broke my heart in recent reports is about a teacher who continually harassed girls from the school he taught for so many years . The teacher only got exposed when one of the girls grew up and realised what was done to her in the school was wrong. Only then, one by one, other girls also started speaking up that they were also victims of the molestation from that specific teacher. But, the saddest thing is till the time that teacher got exposed, that molester had already harassed so many young girls. But, if there had been a complaint response mechanism at the school, the problem would have been addressed several years ago, and many girls would have saved themselves from the crisis.

This is only one of the incidents of teachers molesting their own students that got exposed; there are many schools where girls are not able to speak up as they are threatened about failing exams or their pride. Why do these similar incidents occur once in a while? Is it because the girls are not educated about harassment? Or, is it because the system has not provided any mechanism where students can complain about their problems?