Actually many did - the problem was you couldn’t just “free” a slave and release them into society - they’d end up on the streets and homeless or subject to recapture. So the humane and responsible thing was to just treat them as part of the family and provide for them.
That’s exactly right, and of course the article gets into some of that nuance
The real world is messy when people with Big Ideas start trying to implement them
Children can dream up Big Ideas...but it takes real adults to actually implement them