this is how Dranac disposes of its dead: there's no soil to bury them in and only wealthier folks have access to cremation (or at least authorized cremation, maybe you could still cremate a loved one somewhere in the depths of Dranac's passageways without getting arrested), so everybody else is forced to dump their deceased into the cemetery sectors where they're mixed in with garbage, hence the makeshift grave markers. it's also where all the John/Jane Doe murder victims and dead homeless go, swept away by the authorities.