Bottom line, lack of reciprocating was due to a simple lack of knowledge about the site when I first joined, not a reflection of the reviewers's own material. I suspect other new users may be in the same boat. Some of the free stuff I've read hasn't even received a reply yet.
Yes, this is true. I've changed a lot of language for new users to let them know that if they don't give reviews, they won't receive them. I'll continue to look for ways to reinforce this point. In the Free Group, there will be a certain percentage of users who want to dump their content and leave.