Well I'm not sure why but it mostly happens to new accounts upon creation not older accounts most times plus I still don't know exactly which IPs are flagged and why exactly they got flagged.
Older accounts are already created, so they cannot be banned regardless of what units of evil is associated with their IP.
The evil fee is sort of a deterrent from ban evasion. If an account is banned or nuked, evil units associated with that ip increases, when it reaches a level no one using that IP will be able to create new accounts on the forum, probably cause they are assumed to be evading a ban.
It doesn't however work like that in practice affecting lots of new members who have no previous accounts, hence the whitelisting approach.