Everyone seems to be asking this question. I want to offer two explanations.
One comes from 1977. I was 19 in that year. I was at Southampton University, and already an activist (a social democrat then, probably a little to the right of where I am now). There was a big debate in the students' union. I don't remember the precise motion, but the Liberals and Broad Left (pretty much Labour) supported a motion saying paedophiles had rights that had to be respected.
I was shocked and angry. I got the chance to speak as second main opposer of the motion. There were several hundred in the audience. It was the best speech I'd ever made at the time. It was the first time I realised I was carrying an audience with me. It was exhilarating. But best, the motion was defeated. That was better.
And yet it says something of the time that such a motion was proposed by those too liberal for their own good. That was the era.
But things have changed dramatically since then. So why, still, did no one speak? Here I speculate but it's not hard to do so.
Our society is obsessed with power, and celebrity. Mix the two and people believe a person is quite unlike other people. Though they're not.
And this society is massively hierarchical: power is afforded to those at the top. The rest are meant to obey. It's incredibly hard to break this rule. At work people want 'team players'. Those are the people who will obey, not rock the boat, won't question and know when to turn a blind eye. Because people have learned that this is how to survive we have large numbers of people in this country who know this is what is expected of them if they are to get on - especially if they are also told in no uncertain terms that they will never make it to the top. Far too many people are told that.
I suspect Saville knew that.
These are the people he picked on. They are the people he exploited.
Society does exploit people in these roles in so many ways. And it is power that does it: managers want people who will not challenge them, nor bring them news they do not want to hear. So they don't hear it as they're not told it.
It's why, of course, we don't flourish as we might as a nation. People are encouraged to be ordinary. I know that sounds an appalling thing to say - but it's true. Most of British education has this goal: we don't strive for excellence, the out of the ordinary or real thinking, we just aspire to the mean. And in that environment people will not speak.
Saville knew that too. And so he got away with his crime.
It's also how so much tax abuse happens too, unreported, but widely known.
And until we empower people - to speak out much more widely such abuse will continue.
We have to encourage people to believe they're anything but normal if we're going to stop abuse and encourage the exceptional in all of us, whilst ensuring the constraint within society to stop abuse happening.