The historical artifacts exist independently of the search ranking. Actual bad guys can get a new domain to get a clean slate without taking the old one down. The reason they care about the cost of domains is their domains get a bad reputation immediately and they have to cycle through far more than one domain a year.

If they were going to consistently use the same domain for links while they churn through hundreds/thousands a year for Google, the extra cost for one extra renewal for the persistent domain would be entirely negligible. And on top of that would make it trivial for Reddit/Facebook/etc. to disable all the historical links because they all go to the same scam site.