You need to study your history.
Rome had a majority of its citizens enslaved.
And Rome at the time ruled the world.
The reason Jesus never spoke out about slavery was that at his place, a bigger injustice was going on in Judea. The marginalizing of lepers and sinful as second-class. The Jewish laws that shut such sinners out of the temple and made it difficult for actual atonement.
I know the OP wants to smear Jesus as some kind of failure for not opposing slavery, but there are other things in life. To Jesus, being Jewish was a priority, and he wanted to reform things.
But his followers eventually advocated for the release of slaves.