It took a lot of money and time (1720 – 1740) to build the massive Fortress of Louisbourg on the east coast of Nova Scotia's Cape Breton. A fort designed to retain control of French Canada to the north. Boat loads of money, and the Royal Treasury of France regularly sent pay-ships to Louisbourg to pay the army of workmen and contractors.
If a storm, as are not uncommon in the great Atlantic, were to force a ship off course it could become grounded or wrecked. In such a case a crew might be convinced, willingly or otherwise, to help conceal the great treasure on a nearby Island. Or such a ship could succumb to pirates who likewise would have need to conceal their great fortune.
The same fate could have also befallen other pay-ships such as the one sent in 1746 by the Duc d'Anville to recapture Louisbourg. The great treasure and the goods from the ship were never recovered.
The timeline would be reasonable for a Louisbourg pay-ship but it seems a bit tight for a later ship based on what is known about the Money Pit.