After Independence it was too late.
The proper time to abolish slavery was prior to Independence.
The states before the revolution were independent ao some would have abolished slavery but never all 13.
The American colonies were not allowed to transport slaves from Africa. That was a British, Dutch and Portugese franchise and most slaves went to the Carribbean and South American plantations were they were consumed. In North America the climate didn’t kill them.
The british restricted a lot of movement to the American colonies to support their economy. Spring steel was one so clocks made here had to use English steel or had to be wound evryday like my Chauncey Jerome clock.
If that had been the plan, we would have abolished it when England did, because we would still be part of them.