What is one reason why the east coast has so many bays and islands?

Water released from melting glaciers raised sea level

A bay is a broad inlet of the sea where the land curves inwards. An island on the other hand is a subcontinent of land surrounded by water. Scientists believes that melting glaciers raised sea levels to areas that was covered by land, submerging most of it. It is one of the red flags to the problem that can happen as a result of global warming.