After he switched from growing tobacco to grain? I wonder if that has anything to do with tobacco being called a cash crop?
So then he got rid of his slaves, right? Jefferson and the rest of the boys as well, huh?
George Washington finding slavery inefficient on his own personal plantation is not costing the economy. I mean, it did cost the economy especially later, after all that was the cause of the Civil War, the REAL cause. Should the federal government waste more funding on the agricultural slave owning South or on the manufacturing North that paid most of said funding to begin with? Add more slave States, and it's a further drain. Plus that with added members to Congress, they get to vote themselves more money.
The cotton gin and other such innovation reduced labor needs, making farming cheaper, thus making slavery an increasingly costly expenditure rather than an investment.
But it isn't like slave owners were going bankrupt with the practice but failed to realize it over the centuries. Profits were still made from agriculture to manufacture to sales to exports. And banking and insurance as well. Britain may have outlawed slave ownership in 1807, but it still reaped huge profits off the slave trade.