I dont think it has to do with profit, because each station already have corsairs in it to get the job done. I assume though, that some corsairs wouldn't mind having slaves, but despite that, its generaly considered immoral, even for corsairs - hence the decision. However, this does not mean that human organs themselves are contraband, given you got them through "legal" means. Crete has hospitals and its unreasonable to think we dont need organs.
I dont believe there was a "because" reason, sairs aren't hessians who can use slaves to mine for them.
