Oysters were poor people food in the same era, and like now, many people ate them raw. It has less to do with culinary trends and much more to do with the relative productivity of the lobster fishery. (In recent years, the lobster fishery has been really productive, but prices have been pretty sticky[0].)

Mark Kurlansky's The Big Oyster has some great primary source research on the social status of eating shellfish through the years.

[0]: https://www.nytimes.com/2012/07/29/us/in-maine-fishermen-str...