There was a reason. The story was told from the start that the first main searchers had obtained some treasure map that they equated to being for Oak Island. The story got changed later.
Basically they dug at the place the copy of their Spanish treasure map seemed to mark.
But nothing was there.
Hence to keep the money from investors coming in they could not longer promote they had a real treasure map for a treasure on Oak Island because the map then just proved they weren't looking on the right island.
The detail was then removed which is why the story as told now is full of obvious inconsistencies.
If you are wondering the detail of the search being caused by a treasure map appear published up until the the early 1970s. After that, this detail was totally suppressed by those running the search concession when the story was given to visitors/researchers/jounalists/reporters who went to the island so the money would keep coming in.
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