Because of the way humans evolved, we like and consider 'good' wide open spaces. For our stone age ancestors, being out in the open with broad vistas was safer from predators than closed in spaces like forests. It's why we aspire to having a good view. So, because we associate closed in with bad, it's green and black dragons that get the closed in forest and swamp environments, while various good dragons get places like coast, hills, and mountains. Basically, no, good dragons don't go for forests unless it just happens to be a part of the climate and next to topography that they do like.