...or are even in the hands of the same family?

Still pretty common at least in places near where oysters are grown, I think. My guess would be also that tastes changed over time as oyster fisheries were overfished and/or polluted by growing cities. There have been numerous waves of oyster collapse on the US east coast over hundreds of years, and places that once had them in incredible abundance now have none (though efforts to restore them have emerged).

There are a variety of parallels in the history of overfishing where a given seafood that was once abundant was then seen as undesirable and served to servants or prisoners (lobster, salmon), but today is somewhat of an expensive delicacy.

The other interesting one is celery. I read an article a bit ago about how salted celery stalks were popular around the early 1900's with all kinds of heirloom varieties being served. Quite a few of the menus I have clicked on have celery listed as an appetizer...

I would have guessed nutrition, we live an in age of vitamins and fortified foods. You can get a lot of zinc and other metals from clams and oysters.