When dealing with the unseen, with heaven and hell, the potential for imaginative creation is endless. When you tie this with the need some have to control others, you have an inherent tendency towards punishment inflation.
The wages of sin is a headache.
A year long headache.
A lifetime of headaches.
A thousand years of headaches.
A million years of headaches.
An eternity of headaches.
There is no reason not to suppose these things evolve. The notion, once constituted, is enormously useful for social control and endlessly adaptable.