Why do people join groups online then say nothing, ever!

I think we call them lurkers – at least this is what we called people 20 years ago that joined chat forums on AOL but remained silent whilst the rest of the group chatted about stuff. They lurked in the shadows saying nothing, ever!

I created a group on an online network recently – the group membership began to rise and after a while it ran up to hundreds. Every person who joined had to go through a process of requesting membership then getting an email from me asking them why they wanted to join, replying and so on, not to mention looking for such a group in the first place.

Since the beginning of the group I think about 10 people have commented on or started serious discussions, all the other posts have been about jobs, seminars, events, selling stuff and so on.

Tell me what encourages you to speak out in an online group? I will put all suggestions to the test.