In slavery the slave was not seen as a member of society so he could not buy, what he produced was not much and the expenses to bring and keep the slaves were becoming many.
It would be difficult to keep semi-wage earners on large properties: given the availability of land, they could try other forms of life - becoming artisans, squatters and small farmers, for example - which would complicate the flow of labor to the mercantile company, in which large traders and owners .