The Framers of the Constitution added the Bill of Rights in 1791 to protect individual liberties and limit the power of the federal government. They wanted to ensure that the government could not infringe upon the fundamental rights of citizens, such as freedom of speech, religion, and the press, the right to bear arms, and protection against unreasonable searches and seizures.
Many of the Framers were concerned that without explicit protections for individual rights, the federal government might become too powerful and infringe upon the rights of citizens. The Bill of Rights was added to the Constitution in response to this concern, as a set of amendments that would explicitly protect individual liberties and limit the power of the federal government.
Therefore, the motivation of the Framers to add the Bill of Rights was to safeguard individual liberties and check the power of the federal government.