The bullying report will stay buried because bullying went on for a long time before it leaked. Catherine went to Chuck with her concerns about how the Sussexes were treating staff and he dismissed her. The Palace only commissioned a report privately when staff went to the press. A private report through own lawyers, not a public report, it was theirs, they owned it and they could bury it having promised they'd publish it with "full transparency".
They never intended to release it and never will. They had a duty of care to their staff and failed them, only acting when forced to do so. This is why it will stay hidden, it reflects just as badly if not worse on the Palace.