Why did the important leaders Sam Adams, John Hancock, and Patrick Henry not attend the convention?

Thomas Jefferson, John Adams, and Thomas Paine were in Europe. Samuel Adams and John Hancock were not elected. Patrick Henry was chosen, but declined.

Sam Adams had said he "smelt a rat in Philadelphia, tending toward the monarchy" and he and the others did not believe in some of the things in the constitution, and thought they would just end up where they started, i. e. monarchy