International law also requires intervention, which is why those in government bend themselves into knots to avoid calling it what it is. Because they want it to happen, they want to leave the option open for themselves, and they don't want to be put in a position where they have to stop it or face legal exposure later on. Which under the current "rules based order" they never will
I would say there are incentives to maintain the population of slave labor but they seem happy enough to deplete their permanent underclass of migrant labor