"Nothing new to say" usually implies that the thread has come to a point where it is nothing more than repetition of points already made. People come to a thread, read the title and make a post, without reading the conversation that has taken place.
Sometimes an event with national attention has limited information available to the public. The investigation is still underway and the thread is nothing but speculation.
At some point, if the thread may devolve into, "If I'da been there ..." or "I woulda ...". Then we aren't learning anything more about the topic.
[Edited to add: I will leave this here in view, since many members may be curious about this question. The Gen Disc mods can move it to Site Questions and Tech Support (NO FIREARMS QUESTIONS)