First, the stats you see on Area 51 are general guidelines, not precision metrics, and they're also heavily cached. Let me take a moment and explain why we have a bit of interest in this particular number.
We tell users that they can expect a quality, peer-reviewed answer to their question as part of funneling new users through brief help texts to show them how the system works. We don't in any way guarantee how long it will take for that to happen, but most people have a relatively reasonable expectation that they should get an answer to their question within a few hours, depending on the complexity of the question itself.
There are some questions that simply require a degree of rare or highly specialized knowledge in order to answer. People that ask these sorts of questions are generally aware of this, remain hopeful that they'll get a good answer soon, but also appreciate a good answer eventually. Highly technical sites with a 100% answer rate are extremely rare, if not impossible.
On active sites that get between 10 and 20 questions a day as a baseline, there's always something new for people heavily engaged in the site to do. However, those few unanswered questions that tend to be very difficult can actually help you engage expert visitors that have the kind of knowledge you really want. Having a few around doesn't hurt.
84% is a bit low, but this community is also quite young, and I'm certain that there are plenty of Tor experts that haven't found us yet, or just haven't had time to dig in.
What I recommend you do is go through the list, take perhaps ten of the questions you think would be most likely to interest and entice a really knowledgeable expert into answering and then think of other places in the Tor community that might be willing to help you get light on them.
But don't worry too much about it at this point
I ran a query, and the overwhelming majority of questions asked on Tor Stack Exchange are answered within 8 hours, many less than 8, quite a few between 2 - 4. That's fantastic, because it keeps people coming back with good questions while also looking around for things to answer.
If anything, this is just the impetus to another fun discussion, perhaps identifying places that would help you promote this site by getting tough questions in front of sharp experts, then look at it again in a few months.