The cost of enslaving people is considerable: slave drivers must be paid, escaped slaves must be tracked down and punished. Add that to the purchase price of a slave (and compare that to the cost of HRM registering a new salary earner that the company just hired)
It is inefficient/wasteful. How many of the African slaves in the Americas would have been better suited to other vocations than crudely picking cotton? Or the Polish ones the nazis applied to farming, or the Jews that, in Auschwitz, were put to manufacture, instead of (forgive the stereotype please) finance.
A society based on violence is not a happy one, so people there are not in the comfort zone where their creative juices get going. Google’s HQ in Silicon Valley is famous for its relaxed atmosphere, employees there have a lot of opportunity to play and relax.
Some companies have suggestion boxes where employees can offer new ideas to improve the prices, a new business to enter into, etc.
I would not expect for a slave to put mental effort into optimizing production. “Say, massa, if we rotate this thingamajig by 90 degrees, then we’ll only need 1 screw to keep in place instead of 2.”
Income tax is a very mild form of slavery by comparison, but it is still slavery.
The above explains why the Gulag contributed so little to the state’s income. It was a combination of income-generation (the wood cut in the frozen Siberian forests did serve to supply the state’s export sector) and punishment (a railway line was built at considerable human cost, ,ut never used. Typical for the waste in communist economics).