Witnessed: Ojek drivers whistle at & harass woman

It was a workday, around 3 months ago. I was waiting on the side of the street for my ojek to arrive. There was another office worker near me waiting for her ojek. Suddenly there’s a bunch of tukang ojek that started to collect and whistle and harass her. My ojek came and I had to leave. I am still regretting that I didn’t help her.