I'm a Jew who is active here, but it's challenging and often discouraging. I think I'm still here because (a) I was here early in the beta and (b) I'm stubborn. If I were first encountering the site today, I suspect I probably wouldn't stick around. I also feel that there are enough challenges that I can't, in good faith, encourage other Jews to come here. (I don't discourage them either.)
I hope what I'm about to write doesn't come across as too negative, but since the question asked what is hindering Jewish participation this is going to focus on problems, which may make it sound like all I do is complain. That's not my intention.
The site looks very Christian. The front page -- a visitor's first impression -- is usually mostly populated by Christian-book questions. There are Tanakh questions, more than a hundred in genesis alone, but they're both an overall minority and a minority of active questions at any given time.
Further, even on the Tanakh questions, there are almost always more answers bringing a Christian perspective than ones based on the original context of the text. I understand that certain Christian hermeneutics call for seeing Jesus in the Tanakh and, from the perspective of those hermeneutics, Christian answers to these questions are valid. Knowing that, however, does not do anything to counter the "Christian site" impression, which can sometimes be a little squicky.
Some (sometimes, it seems, many) of the Christian answers cross the line from hermeneutics and exegesis into full-on doctrine. They assert Truth but don't -- and, often, can't -- support those claims. That is definitely off-putting; it runs counter to what we say this site is, but those answers come nonetheless. And get votes. And damage the site. I don't want to participate on C.SE Lite; I want to participate on Biblical Studies (nee BH).
There are some answers on this site (from a handful of users) that outright offend me because of misappropriation -- either they wildly re-interpret Tanakh texts for their own purposes or they claim to be using Jewish techniques when they're not (e.g. PaRDeS). A little truth in labeling would go a long way here.1
Look, we all have strongly-held beliefs; from my point of view certain people here are Wrong, perhaps heretics, and many of you certainly feel the same about me. That's to be expected, and is not a problem. But to me there's a difference between knowing that we all disagree on some fundamental tenets -- and leaving it at that -- versus having Christian assertions of Truth, assertions that are from my POV both wrong and offensive, rubbed in my face. I get enough offensive evangelism in my day-to-day life; I don't need that in my hobby.
I get that there is a chicken-and-egg problem here; to get Jewish perspectives you need users who are Jewish (or, if non-Jewish, interested in Jewish approaches), but to get those users you need content to draw them in. I don't know how we address that.
I have written (checks) 123 answers here to date, I suspect more than any other Jew. That feels pretty significant to me, but it's a drop in the bucket compared to the 2300 answers currently on the site. So a visitor randomly browsing the site isn't going to encounter that many Jewish answers.
Little motivation to ask questions
I've asked relatively few questions. That's mainly because I have a place where I can get Jewish answers to my questions, and I'm not interested in Christian answers to my Tanakh questions. If I had questions about the Christian books I'd ask them here, if I didn't fear that they would be too basic (we're supposed to be aiming at experts). I'm not saying I'll never have such a question, but it's not a focus area for me. The questions I have asked here include:
several questions I tried on Mi Yodeya first (but didn't get answers)
questions about hermeneutic methods (which belong here and not elsewhere) or translation approaches
one public-service question to save a tag
one genuinely-original-to-this-site text-based history question; after almost two months I've gotten no answers (too hard? too boring?)
So my -- and presumably other Jews' -- contributions to the site will come largely in the form of answers, which does nothing to help the balance of questions on the front page.
As Isaac noted in a comment:
SE sites are meant to host and be sustained by communities of experts asking and answering each others' questions. If experts of a particular class see value in answering but not asking on an SE site, then I think it's unlikely that that site will sustainably cultivate a community that includes that class.
That seems to apply to me.
It's kind of lonely in here
My answers generally do ok here. As of this writing all are up-voted; that's pretty cool. I've got a fistful of Nice Answers (no Good ones yet). Almost all of my reputation comes from answers. Even so, I sometimes put a lot of effort into an answer to see few votes and almost no other feedback, and it makes me wonder if it was worth it -- especially when I see Christian-doctrine answers, which are poorer Stack Exchange answers because of their subjective content, get the same or more votes.
I am not whining about votes; I'm one of the top users, after all. I'm bringing this up because it reinforces the "loneliness" of being a Jew here, and sometimes that sense of loneliness makes me say "eh, not worth it" to a question that I would really have to work hard to answer.
I sometimes have the sense that there's a limit to the postiive feedback (votes, comments, etc) that Jewish answers can get here, and some days I wonder if I've hit it.
A lot of what keeps me here, I suspect, is some key people -- people whose answers I almost always enjoy reading (even if they're heretics :-) ), people I have good conversations with in chat, people who are trying to make the site better, people I consider to be friends. That keeps me here (as long as it remains true), but it's probably not enough to draw someone in.
One other thing: I did not know the word "hermeneutic" before seeing this site show up. Seriously. Now it's true I'm not a theologian, an academic, a rabbi -- I'm just a regular person, one who enjoys learning and knows some things. That my answers do get positive reactions tells me I'm welcome here, but I don't know how clear it is to someone like me that his contributions would be welcome, if that makes sense.
1 I downvote these and sometimes vote to delete, which are options available to me as a high-rep user but not to a newcomer.