I just saw that episode too. But I think a problem is that when using oysters in areas that are polluted you really shouldn't eat them. So it'll be awhile before it's a business venture of eating them. I know in NYC they are growing oysters in order to improve the water conditions with no intention of eating them yet.
In NYC before people were messing up the environment just by the nature of building a huge city, there were billions of oysters all around amd the water was super clean.
Then they harvested and ate all the oysters, and the waters became very polluted.
Look at the size of this pile of oyster shells from 1912
