It still does not. Slave labour is very cost ineffective even if you are woking people to death, because costs of infrastructure, guard, kidnapping etc. are much higher than what is gained on not paying wages, also even slaves worked to death have to eat else they would last maybe few days and their productivity is abysmal compared to even serfs and not to mention wage labourers. That’s why ancient slavery disappeared.
There are only two cases where slavery is profitable: First is when there is huge amount of slaves AND the economy is on primitive level, both parts are also important else we would see III Reich use slave labour on even bigger scale, and they largely used them in primitive farming and industry like mining, logging etc. Second is when somebody else, usually state, pays for abovementioned costs like infrastructure etc. and private sector gets the gains, that was also the case of III Reich and is now the case in USA penitentiary system.