Mostly because we're idiots who can't see the hands in front of our faces.
Anyways, I went back and re-read the chapter so far, and
quite a few things suddenly become very obvious. Including much of the sheds history.
Fact One: Monsieur Gravois did not build the shed. It used to belong to a M'sieu Doucet, and came with the land which Gravois bought.
Fact Two:: When Girot last saw it, he noticed nothing odd about it.
Fact Three: While there have been many rumors of disappearances, the workers all think that it started after Gravois got the shed, and that the first person to disappear was his wife, Madame Gravois. They think it's her ghost.
Conclusion One: The shed is not an originally evil place. No ancient burial ground or the like, or at least nothing active. It acquired its evil reputation from some action of Monsieur Gravois.
Fact Four: Gravois, his son Etienne, and the big Souragnien whom I conjecture to be the field supervisor, are all aware of the shed's nature and use it as a punishment or a disposal system.
Fact Five: When we actually see an ethereal resonance of the shed's nature, we see a man named Rene, who looks remarkably like a young Gravois, with a bound woman rather resembling the Late Ms. Gravois, who is bound and begging him to stop.
Conclusion Two: For one reason or another, Rene Gravois murdered his wife and buried her in the shed (possibly alive). This has caused the shed to become a haunted place, and thus M'sieu Gravois has been leaving people who cross him to the spirit of the place (hence the many reaching arms in the vision).
Question One: Why did Rene Gravois murder his wife?
Question Two: What about the murder caused such a powerful ethereal resonance, enough to spark a shed capable of consuming people somehow?
Question Three: If that's Etienne's mother who was killed in the shed, why is he so content with leaving people there and still working for his father? Is he aware of the
cause of the shed, or only of its effects?