Short answer:
Your forum is the exact same as the other 100,000,000. Just less active and less threads. You offer nothing unique that the other 10,000 popping up and closing every single day offer.


So....either offer something unique or get a ton of visitors and hope some convert to members. Problem with getting members is, who cares? It's just a statistic and a useless one if nobody posts. That's the next hurdle. Getting them to post. Otherwise having people join is pointless.

Nobody cares if you have 7,000 members, but most are auto-posters and the rest never even login.