Why is a clam bake called a "clam" bake? Traditionalists expect a classic New England beach-baked feast with said clams as well as lobsters, mussels, shrimp, corn, potatoes and sausage — so I gather from the many historic festival menus along the coast.
Legend has it that Native Americans taught Pilgrims how to bake clams and other sea and seasonal foods — which, yes, sounds just like the Thanksgiving dinner origin story. So perhaps as the turkey dinner has evolved to include the requisite stuffing and regional sides, the clam bake has too.
The New England summer clam bake is best known, but there's also the lesser known Cleveland clam bake in fall.