Upvote:5
It would seem that slavery in Europe was all but extinguished by the Medieval Era - so the Colonial Era slave trade from Africa was not directed at Europe: Slavery in medieval Europe (Wikipedia).
Europe was also more populous than the Americas, with much of the population already bonded as serfs to the noble land owners. There's not much different between a serf or slave, so there wouldn't have been much of a market.
The slave traders were making money from selling their slaves to the Americas, where they would then buy coffee, cotton, and many other goods back to Europe - this is what Europe wanted. It would not make sense for them to curtail their profits by simply shipping slaves to Europe.
Upvote:6
In the Colonial Period, Europe had some ideas about the enlightenment that made slaves unpleasant to their sympathies. For that reason, despite the English having slaves in their colonies, you could become a free man by visiting Britain's shores (there were some interesting court cases related to this).
More important to this era was poverty, which was a big issue in European cities. So there was no shortage of cheap labour; even with the dying out of serfdom. Serfdom lost popularity in Western Europe around the 1300s (though cases remained until the 1500s). The practice was continued in Eastern Europe for a lot longer, to try and fill the gap in the agricultural market that arose with the reduction of serfs. After the Napoleonic wars, serfdom mostly came to an end in Europe, save Russia.
The place where a demand for cheap and harsh labour was in force, was in the colonies with their plantations. Recruiting people from the European homeland to farm this would've been difficult to convince them and expensive to pay them, so slaves were the economical way out.