The English social hierarchy was incredibly big. If there were slaves at the bottom of it, there were also hugely important people at the top, dukes and earls with great houses and huge incomes. The most important American colonists came nowhere near the upper echelons of that hierarchy: in England, someone like George Washington, with an income of about 300 pounds a year, was just another yeoman farmer. As unimportant, non-voting subjects of the King of England and subservient to English law, the colonists could see slavery as a just a fact of life, something that they could not change. When the Revolutionary War removed much of the top of that hierarchy, removed titled nobility in the Colonies, made the colonists their own government, mere farmers like Washington suddenly went into leadership, slavery suddenly became something that could be abolished.. And, after taking up arms because of revolutionary rhetoric about liberty, and creating a more egalitarian society without dukes and lords, for the Colonists slavery was also suddenly an inescapable contradiction, the “peculiar institution” out of place in a free republic.
But if the Revolution had brought in a government that could forbid slavery, many people, including those leading the government, had been making their living from it. The colonies had a primarily agricultural economy, needing a lot of labor, and slaves were a big part. The Revolution did not change that. Some, like Washington, didn’t let the contradiction of enslaved people in an egalitarian republic bother them. Washington had been an enthusiastic farmer and developer before the Revolution. Slaves had been the means to his ends. The end of the Revolution made it possible for him to get on with his plans, and he did so. Like Washington, Jefferson had been dependent on slaves before the War and was dependent on them after it was over. Jefferson , however, was more intellectual, and fully admitted that slavery was an evil at odds with his political ideals.
But he also liked his gracious living: he had a wine cellar, with French wine. He had a large library, and lots of things he wanted to write. He was a country gentleman, and was not going to turn into a merchant entrepreneur. Also, Jefferson was also constantly dealing with debt, and had mortgaged his slaves- technically, he could not free what he did not full own. It was also illegal to free slaves, especially elderly slaves, without providing them with some means to support themselves. Jefferson therefore only freed seven slaves, and all were craftsmen who were likely to be able to earn a living. He likely allowed a few more to escape, without pursuing them.
Admitting slavery was an evil but dependent on it, Jefferson simply temporized. He hoped that one day in the future by popular vote slavery would be abolished.
I congratulate you, my dear friend, on the law of your state for suspending the importation of slaves, and for the glory you have justly acquired by endeavoring to prevent it for ever. this abomination must have an end, and there is a superior bench reserved in heaven for those who hasten it.
Jefferson to Edward Rutledge, July 14 1787
He tried to ban the importation of slaves into Virginia in 1778. and drafted part of the Northwest Ordinance, that banned it from the new territories. He was not alone: Madison, another slave owner, signed on to the Ordinance, said similar things about some day a political solution would be found to end it... but didn't free his own slaves- and Madison was not in debt. But these hypocritical, hopeful Founding Fathers might have actually thought that, with more restrictions, slavery would simply somehow become less and less common, and eventually fade away. They couldn't anticipate that the advent of the hugely profitable cotton plantation in the early 1800’s would make slavery even more entrenched, could never know that, if there was ever a time for peacefully abolishing it, the first years of the republic would have been it.
Joseph Ellis: American Sphinx: the Character of Thomas Jefferson