Again from history, the Roman slavery was an indentured servitude kind of thing. Instead of debtors' prisons, they had this. Palestine was under Roman rule and there were a lot of things in Old Testament law that the Romans did not allow them to do (just like we aren't allowing stonings in Iraq today). Had they been able to, Jesus wouldn't have been crucified, but stoned.
Kinder, gentler servitude.
Sure, that's why Spartacus and several tens of thousands of other slaves risked (and eventually succumbed to) death to fight against their masters rather than just wait until their indenture ended.