How come nobody's interested in joining new clubs on this site?

People might not know about the club yet. Others might know about it but might not be interested in its topic, so they don't join. The best bet is to advertise the club in related clubs, bringing to people's attention. Members aren't automatically made aware of all new clubs, so unless they're advertised or people look for that subject, they won't find them.

People need to advertise their club to get people's interest. And everybody has different interests. You need to have patience.