why Documentary Films about Fringe theories almost always gives Mundane explanations about Them?

I wonder why vast Majority of Documentary Films(both in the Cinema and TV) that dealing With Subjects outside Mainstream Academics like Intelligent life anywhere but Earth in the universe, Cryptids and Legendary Creatures, Anything Paranormal and Supernatural, and Most conspiracy theories are almost always ends up gives mundane explanation about them?

[edit on 26-4-2010 by masonicon]

[edit on 26-4-2010 by masonicon]