On Chrome for Android you can just press 'Add To Home' and it makes a self-contained web app. There are very few reasons to have dedicated apps and a forum isn't one of them.
The forum works absolutely fine on mobile browsers. A mobile app would just be another thing to maintain, and given that DTG struggle to maintain existing releases, I don't think it would be a wise idea...
I’ve added it to my Home Screen on my iPhone. I just it could’ve done with a few tweaks that’s all. Just a thought.