One of the nice things about having your website ranked number one for its keyword is Google will show a dropdown of other links on your site, typically called sitelinks. These links are typically ones that have been linked from other sites so Google considers them important. The sitelinks in the search look like this:

However, occasionally when you expect to see site links underneath a brand name appear, none actually appear, which begs the question why aren’t sitelinks showing in Google search? It turns out if there is more than one domain with sitelinks for a search result, then it will show the one-line links and if there is only one it will show the regular sitelinks for the first link. So if you search Drupal, both drupal.org and the wikipedia entry for Drupal come up and it uses one-line sitelinks for both and looks like this:

Basically it’s up to Google to decide whether or not your site is shown with full site links or not. However, if you are having this problem it means you are getting links.