I just joined our club this year and only have 27 members, of whom only 7 fly. The problem I've heard and seen over and over is that although clubs talk a good game concerning offering flight instruction, too many, if not most seldom, if ever deliver.
Before I get flamed, what I mean is when clubs sell their hobby to newcomers, the sales pitch is something on the order of "We will be more than happy to teach you to fly and at no charge". The beginner gets the impression that he will be able to get help on a regular basis, such as any time he needs help and that help will be for free. But what is the norm is at best, 15 minutes of instruction, once a week. Also, chances are, he is not told of this:
http://webhome.idirect.com/%7eironsidz/instructor.htm
Then there is the assurance that crashing is all but necessary as part of the learning process. All of the above is the main reason membership numbers tend to stagnate.
Then again, it's not out of the question that the veteran flier may not want his flight line constantly congested.
nascarjoe