Every time I open MSE I see that there are 72,000, and counting, questions without upvoted or accepted answers. Why are there so many? Most recent unanswered questions I've seen can be answered. There exist difficult questions, but it seems this site is not really for truly difficult math as measured against the current expertise of professionals. That is delegated to MathOverflow.
Are there too few people answering questions? That seems to be one possible explanation. 72,000 is of the same order of magnitude as the total number of users. Some users answer many questions a day, but I get a sense that most do not answer any. Most are here because they are asking questions, not answering them.
Another possible explanation is that the OP of the question did not make the effort to accept an answer after receiving it. This is understandable. I can imagine coming across something that really stumps me, posting it on a site, receiving an answer and then forgetting about the site's idea of "politeness" because what I really care about is the answer to my question. And the person answering the question screams, "I put in so much effort into answering that question, and I NEVER got the extra 15 points for having the answer accepted. Doesn't the OP care about my score? Or my feelings?" It's kind of a silly question when you put it in perspective.
Of course the 72,000 only includes questions that do not have upvoted answers. A question not having an answer suggests that maybe it's an interesting question that really provokes thought, and sometimes this is the case. But what about questions that do have answers such that all the answers are not upvoted? That could indicate possible indifference among the people doing the upvoting, or maybe nobody ever got around to reading it. A darker conclusion could be that the answers that were given were just bad answers.
Therefore we are displaying this large number that indicates not only that there are too few people answering questions, but also that people who ask questions don't bother to maintain them. Furthermore, it says that many of the answers given are not screened for quality and some questions only get bad answers.
Does anyone have a better explanation for why this number is being displayed?