It's at about 2 questions per day when it should be at 15.
From my experience in academia, history is one of the most dense academic fields in exactly the kind of questions that this site is designed to answer. Right now everything is fine for getting out of beta except for the question density, why is this a problem?
Notice that I'm asking for a specific answer from those who have been in the community longer than me, not soliciting open opinion so much though discussion is welcomed.
We are aware this is a tougher topic than most to ask interesting and unique questions about. This factors into our graduation decision.
Of the 115 sites, History.SE is currently ranked at 72 by questions per day. It's ranked 74 by number of users and 67 by traffic. So it's right around where we'd expect it to be by the numbers. The recent self-evaluation (and my analysis of it) suggest that question about history are harder to ask than questions on other topics. Even so, questions do seem to get good traction on Google (~87% of traffic comes from search engines) and the quality of answers is generally higher other resources on the internet.
There are two ways to look at the data. Either:
The first is the most obvious mechanism since you can't have questions without people to ask them. So let's jump straight to the second:
Suppose you are a brand new user to History.SE. Maybe you came from another Stack Exchange site or maybe you found an answer to a question here when using a search engine. If the site looks good to you on first contact, you might start looking around. The obvious first place to start is the active questions page (which is where you go when you click "History beta" on the upper left of the page). Hopefully there are some interesting questions to read (such as Has there ever been a truly multi-sided war?, which was recently highlighted by the Stack Exchange Facebook account).
Ideally, a new user will find a few questions that are interesting and maybe be inspired to ask or answer one themselves. But it's probably more realistic to assume they will be distracted by a cat video someone posted somewhere else. If they ever come back, it would be helpful to see some fresh content. New answers on old questions can be helpful there, but the best thing would be a fresh question that the new user is interested in and might answer.
You can make a very similar argument for traffic with the big difference that it's Google, Bing, Yahoo, etc. who come back to visit the site. Search engines like fresh content since it's a sign the information is being curated. New pages (which is what a question represents to the rest of the internet) opens up new search keywords that help people discover the site. So the rate that new questions are asked correlates with the rate that search engines drive traffic our way.
Therefore the very best thing you can do for this site is to find an expert in history who needs an outlet for their writing. But the next best thing you can do is ask a great question every now and then. In many areas of life the Field of Dreams approach just won't work. People won't miraculously show up at your cornfield just because you built a ballpark there. But it can work on Stack Exchange. If several people decide to ask a question or two a week, you could probably raise the questions per day a noticeable amount. It might be a temporary effect, but you might catch the next great contributor on History.SE.
15 questions a day, by the way, isn't a scientifically determined number. Our current gut instinct (based on existing sites) is closer to 10 per day. Skeptics, which has the most restictions on participation, gets by with about 4 a day. One of the projects I'm currently working on is figuring out how much extra participation asking questions produces. I hope that among my findings will be more refined estimates of what question rate signals a healthy site.
Coming up with history questions is more difficult than say coming up with questions for StackExchange for a couple of reasons.
The relative size of the historian market v. the programmer market, where there are far less people that are engaged in "history" than "programming."
The lack of immediacy of problems in the field of history. For example, rarely is someone in a time crunch that they really need an answer to some history question in a day or two. Conversely, in other disciplines people commonly pose questions that are time-sensitive.
The fact that for many of history's questions there is no "right" answer. Whereas, if I post on the math stack I'm going to get "right" answers.
Also, like Yannis said, Wikipedia.
Almost every time I wanted to ask a question here, I found the answer (in 5 minutes or less) simply by searching Wikipedia. This, I think, is the main reason we don't get more questions.
Wikipedia's eaten the trivium end out. Which leaves the causative questions (Why did... How did...?), and historiographical questions (Why can we say that...? What makes it legitimate to say that...?). These questions are hard to write, harder to write well; hard to answer, and harder to answer well.
The real issue here, I think, is that SE is first and foremost a site to help software developers get answers to questions. Yes, it's expanded way, way beyond that, but you have to consider its origins. Personally, I'm a software dev and I got into this site specifically because there's a subsite that deals with my specialty (SharePoint, if you care). Anyway... most people who work in software development have a BS in their field, which required them to take lots of science courses, so one can understand why the sciences are so popular. Additionally, there is a lot of bleedover between software development and fields like mathematics (graphics-based stuff like games in particular can get really, really mathy) and physics, and a lot of scientists have to dabble in programming in order to create the tools they need to run experiments effectively.
Then there is the relative popularity of forums like rpg.stackexchange and the science fiction section. Not to get too stereotypical but hey, I'm kind of a nerd myself and I am definitely into at least one and at times two of those things. It's not that surprising, I don't think, to see that a site devoted primarily to software development and IT related issues is going to also have a lot of people into RPGs and the like.
History, though, is on down the list. This isn't to say that nobody's interested in history, but the cohort that comes to SE to figure out how to add a stack panel on a SharePoint site isn't necessarily going to be heavily into history. I mean, I am, because everyone's different (and in fairness my background is about as weird for a programmer as it gets, I think), but I certainly don't think you can expect the same level of enthusiasm for this area.
Another factor to take into account is that many questions have so many tangential connections with other SE sites (like politics or religion) that they end up being asked and answered there, and often migrated from history.se to politics.se or religion.se. Others get closed rather rapidly because they're asked in such a way as be because they're highly controversial and leading (think holocaust deniers asking clearly bogus questions to push their agenda).
