You can't simply make something up and present it as truth. Leaving those tweets up in no way implies a continued endorsement of their content. You have no basis on which to make that claim. One could easily make the counter argument that if he had deleted those tweets he would be criticized for trying to hide from his past.As I've already explained twice: not deleting the tweets, even through laziness/negligence, implied a continued endorsement of their content. Yes, the tweets are years old, but they were left up until a few days ago. Ergo, from a certain point of view - probably the deciding one, in this case - he continued to make those jokes until a few days ago.
The far more likely explanation is that the man has 20,000 tweets and never saw a reason to dig through his archive to delete the stupid shit that he said in the past.