Toxins, radiation, pollution, and disease
Nearly everywhere is either lush greenery that’ll kill you or a radioactive rock. The few habitable areas are heavily polluted.
Ultra-polarised rich and poor
The proles are packed in like sardines in appalling living conditions, and disease is rampant in the slums, while the rich elite use them as an expendable resource, selling them as slaves in all but name. This has the added benefit of reducing the overcrowding, keeping the world sustainable, but no-one seems particularly grateful.
What doesn’t kill you…
There are resources, medicine from the toxic vegetation, and radioactive materials, but they’re difficult to refine, preventing any large-scale harvesting.