"Due to a loophole in the system, people can escape hell and get to heaven after death. You go to hell and all you see is Satan, just sitting there playing the harmonica. Everyone left him and now he’s all alone." -- Gallifreya
Jean Paul Sartre said that hell is other people. He could not be more wrong. Though other people have their disadvantages, the true hell is loneliness. Hell was made to be vast, with room to every sinner in existence. It was made to be unpleasant. It has room to contain every nightmare.
But sinners are sinners for a reason. They lie, cheat, and steal. And all the other things. It's no great stretch for a soul, once in hell, to immediately look for loophole. After all, what is sin without redemption? So all mortal sinners find their way out of hell. It takes time and effort, but time, at least, is meaningless in hell. Effort, however, is triple.
Nevertheless, eventually, all souls leave hell except one.