Because we had a good thing going, and scientists/politicians screwed the whole thing up.
From the article:
From 1987 to 1996, harvests in the United States increased nearly tenfold, and there were a half-dozen companies in Portland processing dogfish.
By 1998, scientists found the spiny dogfish stock had fallen below the minimum level determined to be sustainable, and imposed strict annual catch limits to help the stocks recover.
In Maine, the dogfish catch peaked in 1990 when fishermen landed 6.4 million pounds. In 2013, just over 100,000 pounds were landed.
The Portland processors all either shut down or moved to other ports, said Walter Barrett, general manager at Seatrade International Co. of Portsmouh., N.H., one of only three companies in the U.S. that processes dogfish.
In response to the growing population, federal regulators last year increased the quota from 41 million to 50 million pounds annually for the fisheries in New England and the mid-Atlantic region, with a maximum possession limit of 4,000 pounds per fishing trip. Although there are plenty of dogfish for fishermen to catch, the demand for dogfish in Europe has collapsed because the Europeans have replaced dogfish on the menu with other fish, Barrett said.