Because the Gulf shrimp are seasonal and a small part of the overall shrimp consumption. My local Central Market had jumbo fresh gulf shrimp @ $18.95/lb last week. 16-20 fresh gulf shrimp were $13.95 at HEB and there isn't an HEB within 25 miles of me. I live in the Dallas area where transportation of fresh shrimp is not prohibitive. Much of the rest of the country doesn't have really fresh shrimp available.
I expect the quality of the NS shrimp to be top shelf and people will pay for it. I have tasted their shrimp and they were very good. I have had fresh gulf shrimp just off the boat in Destin FL and these were as good or better.