Speaking about African Slaves in American- slaves were expensive. I think it’s reasonable to draw a parallel between industrial farms and plantations. An industrial farm has big tractors and automation; small farms have small tractors and milk the cows manually.
Capitalists (ie those who earn money from the capital they already have rather than those who work) would be slaveowners and slave ownership would drop off as wealth drops to middle classes - the middle class would own fewer slaves or simply hire servants.
Geography is also a factor; the American South normalized chattel slavery of Blacks to an extent greater than most of the world.
But there’s a long history of slaves around the world that’s not reasonably captured here.