They bring together people at a platform where the shared responsibility of certain experiences relieves them and encourages them to discuss about things that bother them. It helps to develop a stronger narrative around mental health which is a required.
Mental health is not as obscure as we read the quoted statistics as, people are interested to know, willing to seek help. Overcoming stigma does not always mean making your problems vocal to everyone but it can simply also be silently seeking help. Stigma is to stay for years to come, what aspects of us can we work upon is the real deal.