Without speaking to my own judgments of historical candidates, my impression is that people very often vote (in US primaries and elections at least) with an attitude of ‘ugh well it can’t be Alice, so I guess it has to be Bob, even though he is evil as far as I can tell’ rather than, ‘wow, Alice is one of the most shining examples of an excellent leader and all around good person I have ever witnessed, but I just have to vote for Bob because he is astonishingly even better, and when I see him speak it just makes me cry because I can’t donate money to his campaign fast enough’.
There are like 150 million eligible US citizens to choose from for president, and in my experience many people generally inspire excitement and warmth in others, and are reasonable and knowledgeable and good. I admit I don’t really know how this whole system works, but if it’s some kind of popularity contest, with this many entrants, shouldn’t the results be reliably almost superhumanly likable? (Which is not to say superhumanly deserving of being liked, or superhumanly competent at running the country.)
A non-obvious but plausible category of answer is that such people really are superhumanly likable, but that the situation nonetheless leads to them seeming not so.
Another is that things were different not so long ago, and recent times are a weird aberration. (I welcome insight from anyone who was paying attention in the past.)