IMO, the size of the global population is fast becoming unmanageable because of its exponential growth. There are more consumers than producers in the world and it's getting worse. There's only so many natural resource on this planet. Elite like the cheap slave labor but the sheer number of slaves is just too much now to sustain, so they're quietly getting rid of the rotting low hanging fruit and keeping the more valuable ones around. Yet, there's not enough resistance to pose a threat.