A google rank at zero and lots of 2 hop routes to your site that google can either penalize for being an accurate historical record or not is better than a rank of zero and a domain that has never been in historical artifacts.
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.