Since so much of the literate, conscious slave trade comes from societies of Central Asia (apparently also elements of Sweden and England, and of course the Portugese).. I was curious and asked an observant Muslim here about slavery.. he just looked calmly and replied "it was time for it to end" .. I got the feeling that the Muslim world had some kind of internal reckoning, and did (mostly) end the slavery trade at a certain time, similar time frame to the Civil War.
From the outside, not a specialist here.. it seems like the remaining modern slave trade is mostly driven by raw commerce.. like the fishing boats for example.. Zooming out, it seems like selling known-addictive drugs has similar drives..