The industrial revolution gave the common person more power and leverage over those that governed them.
The common person knew the evils of slavery. It is covered in the bible and the least educated would still have some knowledge of the bible. Many religious people in slave states started arguing that slavery was just and the right order of things but this was a newer idea.
Slavery impacted the commoner as it pushes labour prices down. So even without the moral argument there was a economic one.
Slavery hasn't ended. American slave plantations did, but slavery didn't. There are more slaves now than ever. We could end it but cheap consumer goods keeps it going.
The Bible condones slavery. And many slave holders invoked the Bible to justify slavery.
From Frederick Douglas' first autobiography:
Were I to be again reduced to the chains of slavery, next to that enslavement, I should regard being the slave of a religious master the greatest calamity that could befall me. For of all slaveholders with whom I have ever met, religious slaveholders are the worst. I have ever found them the meanest and basest, the most cruel and cowardly, of all others.
Which dovetails well with the famous quote from C. S. Lewis:
Of all tyrannies, a tyranny sincerely exercised for the good of its victims may be the most oppressive. It would be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience.
A lot of Christian slaveowners "justified" themselves as helping their slaves by "saving" them, or whatever. White man's burden and all that rot.