Visitors but no members

[batman]

Have you checked precisely that the visitors are real person and not bots? It happens that you see a plenty of visitors in your forum board but actually when you see through your analytics there are no such visitors.

And secondly you said that your forum you founded is in last year. So, my guess is that it has not much content comparing to the other forums in you your niche. People often don't join forums when there not much content or not much members, or not much of activity.