Our second weekly-topic-challenge got remarkably little attention after a relatively successful first weekly challenge. At least two possibly courses of action come to mind.
First, we could use regular banners appearing at the top to announce the topic. Despite this being against official SE policy, other sites have also found that banners are very helpful if not necessary to advertise the existence of a topic.
Second, we could extend each topic challenge from weekly to monthly. For a site such as QF, where relatively few independent topics truly exist, a monthly topic may make more sense. There's also a great deal of overhead for me involved with setting up each weekly topic, and transitioning to monthly would make that overhead a lot more manageable.