What a time of upheaval William’s reign must have been. He overthrew a government and entire ruling class, and turned society upside down - removing the Anglo-Saxon ruling class, replacing all the clergy, turning land over to loyal Norman (foreign and French-speaking) nobility, and then trying to find and strip as much wealth as possible to fight rebellions, fund his new kingdom, and its various wars.
If you had money, the only thing you could do would be to bury it.
I wonder if William attempted to confiscate the coinage of the previous rulers and remade them with his own image.