Statistically speaking, if the cast has majority futa characters, then people are going to pick futa characters as their favorites just due to both lack of options and the likelihood that at least a few futa characters will appeal to them. There's also the self-selection bias, as anybody who likes the game enough to have favorite characters is at the very least tolerant of futa characters (of which I seem to be in the minority here. Futa is ew, fight me nerds.)
I know you're taking the piss here, but it's actually a problem that all of the Dev Polls have. Of course futa and female characters are going to win out, that's all there is in this game and the most content has been put into these characters. Their moaning about how nobody wants to write male characters is a problem they've created: there's almost no male content, so people who enjoy that sort of thing aren't going to become fans of the game and demand for more male content. The polls might be technically correct, but they don't tell the whole story.