Best reasonable guess I've seen so far ... there are likely millions of catholic voters (for instance) who would prefer not to vote fot hildebeast but feel uncomfortable votiing for conservative values, so Rudy would be a viable 'reaganesque' alternative. Past landslides must have had something similar at play.
Comparing Rudy to Ronald Reagan is practically blasphemous. Besides, Reagan drew lots of Catholics and other Democrats despite his conservatism. I can't see why any serious Catholic would be enthusiastic about Rudy at all, and people who are not enthusiastic often just don't bother to vote.