A lot of people cite Herculaneum's demise with the growing success of the Wegewood Staffordshire potteries. But Wegewood were already doing well by 1796 when Herculaneum was established. From 1806 - 1820, the H. potteries experienced steady growth.
No one can agree on what caused the factory to close, but we know that other neighbouring industries were attempting to sqeeze them out by planning to purchase the land around the site. Talk about a Herculaneum Dock Bill, I think, was the final nail in the coffin. Fighting local industry is one thing, the government is another. I think they cut their losses and closed the doors.