Well it may help understand if youlook at how the people were treatred who did report him when he was alive. They were ignored and people who brought it to Saviles's attention were threatened with libel and effecetively he blackmailed reporters etc with the loss of charity money.
Newstalk asked him about allegations in 2007, and there were others who reported it.
If you understand how abuse occurs - someone in a position of power and trust.
If you understand the effects on a victim of the act and it's consequences .
If you understand how a victim is viewed with suspicion and blame (as seen on here) with the doubts of making people believe a person in power is guilty.
If you understand the fear of the threats the abuser makes.
If you understand things like these then perjhpas it's not so hard to see why some victims waited.
But remember, some didn't . They complained but were ignored.
Those who were not victims, but knew - they are the ones who need to be asked 'why not until now' not the victims themselves.