I think it comes down to a 'trust thing'. Managers have to prove to their reports that they are trustworthy. Until the ICs know that the manager will actually listen, let alone do anything, without the ICs job becoming more at risk, then nothing will come out.
As for how to build trust? That's a whole other blog, not just a few posts.
As for how to build trust? That's a whole other blog, not just a few posts.