They chose what seemed like a reasonable path at the time. They restricted importing slaves by ship in 1794, just 6 years after the Constitution was ratified.
https://en.wikipedia.org/wiki/Slave_Trade_Act_of_1794
After 20 years, importing slaves was banned.
https://en.wikipedia.org/wiki/Act_Prohibiting_Importation_of_Slaves
It was reasonably thought these measures would lead to an end of slavery without needing a war. That proved to be a false hope, but it was a reasonable approach.
https://en.wikipedia.org/wiki/Slave_Trade_Act_of_1794
After 20 years, importing slaves was banned.
Hard to square that act with the Constitutional provision prohibiting such acts. I guess they were ignoring it back then too.
It was reasonably thought these measures would lead to an end of slavery without needing a war. That proved to be a false hope, but it was a reasonable approach.
Once again, blame Eli Whitney who made it profitable.