RE:WhyIt's because the last substantial news release from GHG happend back in early January - other companies are much better in that regard and keep investors much better informed about what they do etc.
Once GHG releases some proper news and not just a bunch of marketing material like in the last few weeks it'll catch up easily and quickly with the other stocks - and GHG has certainly some interesting stuff in the works and much more longterm potential than most companies in this sector, so it's really just a question of time until we will see some progress.