"Why do mainstream media (at least some of them) not publish this story? Because after a quick follow up they have decided that the source is completely unreliable."

The fact that some mainstrain media outlets fail to carry a story can have many reasons. One of them is indeed that they have followed it up and decided that the source is completely unreliable; but there are all kinds of other reasons which can apply as well.

If it now appears that this video was faked in at least one significant way, it becomes more plausible to question whether it may have been faked in other ways.