Reportedly they voted for him, because he was an actor who played good guys, so people expected him to stay away from big politics.
Idk if he came up all on his own with the idea of becoming president by first playing one on TV, but I've got to admit it's absolutely brilliant.
The logic seems to be that if he's played good guys on TV, it means he already knows what common decency looks like to regular people, unlike the hardline nomenklatura gangsters who live by their own sort of thieves' honor.
Fascinating approach, and one common to East European worldviews: "these people are evil because they don't know how to be good". It's a supremely compassionate view, even if it's proven more than a little counterproductive over and over.