After learning from Tom Riddle's diary that Hagrid might be connected to the attacks, Harry had already decided not to ask Hagrid about the Chamber of Secrets unless another attack occurred.
In fact, he had no idea how to bring it up to Hagrid anyway, so he simply pretended he knew nothing about it.
Unlike Harry, Hermione was still persistent in her search for the truth. She finally found an opportunity to tell Albert about the secret Harry had discovered in Tom Riddle's diary.
Chapter 563