Ghouls were and had always been the most looked down upon creatures of Hell; mindless and hideous with a forever unsatisfied hunger for flesh. Failed children of the devil, many stories called them, since the son of the devil was a ghoul himself.
The truth, however, is they were indeed failures but only to themselves. Ghouls are humans, who by choice venture into the flames and darkness for the sole purpose of becoming vampires, but most are creatures of Hell sentenced to death.
There are a few humans that succeed and a few creatures that become hybrids, but most die a painful and slow death to be reborn as flesh-eating monsters.
Being a ghoul is much worse than being dead, there's no peace even after the body decays and rots. It was the worst punishment issued only to doers of serious crimes. Only the craziest of humans would take the risk!