The most common reason is that BurstWriter does not have real content to ground topics on yet. Topics are generated from your actual site — your WordPress/Wix content, published articles, or Search Console data — never guessed from your domain name.
If your CMS is not connected, or the site has not been analyzed, there is nothing to build a strategy from, so the queue stays empty rather than filling it with junk. Connect WordPress (or Wix), confirm your site identity, and run Re-analyze — topics should appear shortly after.