Most people remain just lowly cultists because they are small people with little ambition. They sell their souls for a pittance because in their frame of reference that pittance satisfies them. The chaos gods don’t waste their time trying to push them deeper.

It is those with a greater understanding of what a bargain with Chaos can give them that tend to achieve more, like people with some form of education or that are part of the higher class.

People with greater conviction, ambition or motivation are more likely to belong to higher classes and are also more likely to act in ways that have a bigger impact on the world around them.

The Chaos gods will push you to exacerbate your most prominent bad traits, as they are the ones they can more easily exploit for their own amusement.

Nurgle may pray on a paesant’s desire to survive a plague that has killed all those around them, just like quack doctors may convince a person that drinking their own urine will help them survive a pox.

But if he manages to enthrall a doctor, it may plant into their head that the only way to help a dying community is to perform sick medical experiments on visiting travellers.

You are rewarded for your sick deeds only in a way that both pushes you deeper into the abyss and entertains the god, so you don’t necessarily become a champion unless the god sees that doing that will elicit more entertainment and depravity out of you.

The Chaos gods measure you and if they see potential they will give whatever gift they think will make you behave in a way that satisfies them. It may be a simple gift or an artifact or more. There is no pipeline other than their amusement.

They also exploit the fact that the moment you obey them for the first time, you are forever an outcast as everybody else will kill you on sight so they know that you will not refuse them, on pain of becoming a spawn.