In 1782, the Virginia legislature past law allowing a master to free a slave without requiring state permission to do so. In 1806 the Virginia legislature passed law requiring manumitted slaves leave the state within one year of their freedom. Jefferson could have met these requirements if he had desired to.
Washington from 1793 on wanted to free his slaves (but half of the slaves at Mount Vernon were entailed to his wife's estate and he could not free them). It was a difficult process because he needed to keep his plans secret, but how to prepare the slaves for their future life as free persons while they were still slaves? How does an adult who has just followed orders all of his life suddenly learn how to make smart decisions?
His will provided that his slaves be freed at his wife's death--Martha ordered them free at the end of 1800 (to remove any incentive for any of them to try to kill her). Reportedly most of them did not fare very well as free persons. Life for free persons of color in a slaveholding society was not easy--the slaveholders did not want their slaves to see free black people enjoying a prosperous life.