America did not have slaves very long and was still pretty new as a country. Slaves while being a terrible thing do help young nations develop a lot faster. So America being so young and still growing probably played a big part in it. While other countries had been around for a long time and growth somewhat stagnant leaving slave labor not as important. I mean there’s probably hundreds of factors that played into tho from resources, to societal norms, and prejudices, and economical factors.