Being available with a correction allows anyone who has seen it that shares it to another person, so long as the person told cares about authenticity, to go online and find out that in reality XYZ were incorrect about the story. Removing it from history either allows the prior person to spread misinformation to those that will not research it, preventing them from correcting the person telling the story or learning the truth on their own.

If they don't remove it then redditors will link to it and confuse readers for years to come. At least they should put a banner at the top saying it's retracted.