It simply is not cost affective to cover stories from independent sources.
While mainstream media is led by profit, ratings and popularist culture and filtered by the current political climate, Alternative Media is lead solely by the convictions of the campaign and film maker.
Due to the political nature of film, partisan film making, especially where the subject is close to the film makers hart, tend to be the norm, rather than the exception.
Activists are generally doers - rather than watching television and thinking about the world they will put there energies into doing something 'active' to change the (political) situation.