I've observed this since I've been on Chemistry SE and I've realize that even though some questions are really good but still they are not answered. People on Chemistry SE mark them "related" but sometimes the question that is being asked has no relation to the "related" question and nobody answers them. Also, they don't get any upvotes or much comments so that the question is in the active tab and eventually the question gets lost.
Why does it happen so?
When somebody asks a question on SE, he/she expects to get an answer. What is the point on asking a question when it gets lost in the stack.