As T.E.D. mentioned, a large part is due to other excellent sources of historical information such as Wikipedia. But also, I really think we are too harsh on some other kinds of questions.
Questions that can be answered historically
The great thing about history is that to be an expert, you also need to know numerous other fields well. One corollary is that many questions that don't seem to be about history, can in fact be answered well by historians.
For example, a recent question impressed this upon me:
Was the Flakpanzer IV used against infantry? If not, what was?
There are currently two good answers; one answered the question by analysing the Flakpanzer itself, and would not be out of place on a purely-Military Q&A site. The other answered the question via historical accounts.
And yet there are two close votes as of writing. My suggestion: go easy on these! Instead of asking, is this about history? let's ask, can this be answered using history? We should welcome more questions like these because they tend to attract laypersons into learning more about history.
Analytical, subjective questions
I think we shut these down too swiftly largely due to existing SE culture, namely one of the stock close reasons: primarily opinion-based. This reason works well for highly technical, "hard" subjects like software, but is unsuitable for "softer" subjects. History is not just a list of dates and events, the true value is in its analysis of motivations and interests, so we're missing out on a lot.
Not that I want every random schmo putting in their 2c about who started WWII or whatever, but expert insight by professional historians or backed by historical evidence is what I really find interesting. We should be more like sites like Programmers.SE in this regard, in that subjective questions are welcome as long as they draw from professional analysis and are backed by evidence. Feel free to downvote crap but let's go easy on the close votes.
For example, I really enjoyed a TV lecture series by Yi Zhongtian about the Three Kingdoms period, and contained gems like "was Zhou Yu a jealous man?" Which seems like the kind of trivial, subjective question we love to close, but it was answered by drawing from records of contemporary appraisals, opinions of historians as recorded in sources like Annotations to Records of the Three Kingdoms. Whilst not definitive, as some put it "we can't read the minds of dead people", it is very interesting nonetheless and is definitely related to history and can be answered by historical study.