Because only in the USA was a large percentage of the population willing to launch a bloody rebellion to protect it.
The war freed people that were definitely not ready for total freedom.
Arguable but let's run with that anyway. By 1861 slavery had existed in what was to become the U.S. for almost 230 years. In all that time no effort had been made by the slave owners themselves to prepare their chattel for life after slavery. No attempts to prepare them were ongoing in 1861. There is absolutely no reason to believe that any attempts would have been made had the South won their rebellion or if the rebellion hadn't taken place at all. So according to you slavery should never end because the slaves would never be ready for total freedom.
Slavery was bad but turning a uneducated childlike person into the world was cruel.
How many uneducated white Southerners were there? They managed to fend for themselves all right. Or would they be better off in slavery as well?
Most became share croppers for the “hated” whitey ex-owner’s land.
Because that was the closest the "hated" whitey could come to re-establishing slavery.
There were some attempts to prepare some slaves for freedom.
Few, and rare, but some. In New Jersey slaves below a certain age had been legally converted to apprentices, to be freed after completion of their term of apprenticeship. Slaves over a certain age were converted to permanent apprentices. In 1860 New Jersey had a total of 18 ‘permanent apprentices, and so, by come ways of counting, could be considered one of the slave states.