I think the software limitations are a big part of the problem.  In particular, how comments are integrated with questions and answers.  The comments appear to give an opportunity for people to have a conversation, but this is discouraged.  Trying to have a conversation and getting shut down is not welcoming.  The chat feature is not threaded, and so it useless for anything but synchronous communication.  I think the site would be much more welcoming if instead of the current comment system, there was instead a threaded discussion forum associated with each question and each answer.  In particular, I think people would be much more comfortable participating in the forum than the QA, but forum participation could serve as a gateway to QA activity.