Currently we are using the built-in Drupal commenting system on this site, which requires that people get a drupal account to comment. This seemed like the right thing to do when the site was set up, and we wanted everyone to have accounts so that they could also more easily send letters to their MPs.
I now wonder if the extra step to sign up, and the use of a simplistic editor forcing people to use HTML encoding, is no longer the right choice. From the comments I see on Twitter, Google plus and elsewhere talking about articles from this site, it isn't a lack of interest that has meant there isn't comments here. It is likely the commenting system.