Bcs primarily it wasn’t a war on slavery, just on profiteering of socialite giants. The USA/north industries had more economic prosperity without slaves (more “people” = higher consumption), the south was spoken by economic powers with high slave labour.

Yes there were activists against slavery, but that wasn’t new, nor did they affect the war iirc/afaik.

And the war industry was infantile (for the last time) at that point.

So after the fighting stopped, there was no reason to proceed with regular after-war stuff (changing & defacing leadership & ideologies, taking guns, instituting mandatory reparations, paying war debts, etc) as long as the economy functioned & recovered. The south kept the guns & their beliefs. And the slaves (just like in the north) entered the lowest economical class which is on average the reason why even today black people are statistically poorer. And still facing the same flavour of racism.

Humans are just disguising. A random product of a very specific evolution path (we have a smol gene pool/variety).