At least partly due to lack of feedback on accuracy. I don’t know about you but I don’t necessarily ask everyone I meet their political leanings, so it’s hard to train yourself other than through stereotype.

Worth noting the human guessing was not on the same data set, but I believe the machines are going to beat us at this in general.

My guess would be sampling bias. Most people base their model on small geographically restricted samples, and are heavily biased by media. It is possible that some people can repeatedly perform better than 55%.