Outside of cotton and sugarcane, slavery was becoming increasingly ornamental. Even the use of slaves in tobacco cultivation was in decline as it did not adapt well to a gang system.
Rigid racial slavery of south was. If not for international pressure and policing on part of Europeans and western world it would stay more profitable in its “classical” or less “racist” forms(you allow more actual social mobility).
This helps keep up the divide and conquer tactic. Like “house” slaves “field” slaves not always getting along or liking each other.
Additionally, reopening or continuing the Atlantic slave trade creates a “Tower of Babel” language/cultural division between slaves. It keeps the ethnic, language, and religious divisions stronger among slaves making it harder for them to organize then second, third, or fourth generation local slaves. Important to preventing slave revolts as well as keeping price of slaves down.
The “Golden Circle” and pro slavery organizations in South likely did tend the above or at least some in it.
https://en.m.wikipedia.org/wiki/Knights_of_the_Golden_Circle
Also this can’t be emphasized enough and could easily tie to international trade mechanic but geography aka distance is important to labor. Look at areas that use African slaves. They are more tropical to sub tropical(they survive better then most whites especially from Isles or Northern Europe) and two they are closer to those areas while the north is closer to Europe then Africa so “importing” indentured labor from Isles or cheap labor immigrant labor from Europe is more ideal and practical.
Slaves do need a price tag added to them for game because while of course it’s dehumanizing they did treat them like livestock which I am guessing is “goods/products” in game even if living thing.
For example, importing new African slaves and local American ones as well to Texas, Mexico, Caribbean, or Central America is much more practical and affordable then sending them to Alaska or Minnesota or North Dakota where more likely die in winter.
Most black Americans don’t leave south in mass until world war 1 and immigration limits created a demand for labor in north but lack of immigrants so they looked towards cheap labor both white and black Americans from south.
Important the Great Migration of Black Americans have been in full reversal since the 80s and 90s. Most are leaving New York, Detroit, Chicago, and even California for Atlanta, Texas, Florida, or the Carolinas now ironically. Most white migrate labor from south already did this decade or two before black Americans did because the “taboo” of moving to place like “Mississippi” has not change in public consciousness of black Americans until very recently. Whites who left south only left for economic reasons. Many would later come back.