This is because the business department will try to force admins to ignore requests to remove spammers as the spammers generally pay decent money.
By blocking everyone, it forces the ISP to get off their ass and kill the spammer irrespective of how much they are willing to pay.
https://blog.sucuri.net/2021/02/uceprotect-when-rbls-go-bad....
ISPs are now so sensitive to not allowing spammers that the RBLs can't make money from it anymore.
This is because the business department will try to force admins to ignore requests to remove spammers as the spammers generally pay decent money.
By blocking everyone, it forces the ISP to get off their ass and kill the spammer irrespective of how much they are willing to pay.