Perhaps because when he was alive the few who did come forward and tell of what had happened to them weren't believed, and let's face it, who would believe a young girl in the 70's against a family favourite tv presenter and multi million pound charity campaigner? Very clever.
But now as the belief rises that these girls/boys/ladies were abused, that gives hope and freedom to the others that they can also now release this burden that has been weighing them down for so long. It may not matter to them whether or not they can get justice, it is just important that they know when they speak out they will be believed and the blame can be removed from them.
When a young person is sexually approached by an adult, it leaves them in a state of confusion. They are convinced they are to blame, somehow it is there fault and leaves them with such embarrassment and shame it makes it almost impossible to tell anyone. Such is the power an abuser has over their victim. And if there is the slightest hint they will not be believed they will not risk that embarrassment and shame of speaking out, and they will carry that intense feeling of guilt inside them until such time as they can speak out. For JS' victims it seems like that time is now
You may be thinking there's no point talking now because he can't be prosecuted, but there is every point. As soon as they are believed they can start to heal and be released from the guilt and shame that has lived with them.
Often abused people are unable to conceive 'love', unable to give it and feel unworthy to receive it; but God loves us, no matter what we may think of ourselves. Whatever we have been through in our past, whatever we may face in our future, nothing can separate us from God's perfect love for us.
Romans 8:38-39 (NIV)
38 For I am convinced that neither death nor life, neither angels nor demons, neither the present nor the future, nor any powers, 39 neither height nor depth, nor anything else in all creation, will be able to separate us from the love of God that is in Christ Jesus our Lord.