I feel like people are mostly just voting for their favorite game, not for the best boxcover.
It's inescapable with this sort of thing, really. You're always going to have biases when polling the general public. Sometimes that's "favorite game" bias, others the assumption that a game does (or doesn't) "deserve" to win a given poll for some reason, and sometimes it really is just an issue of reading comprehension and clicking a button because there's a button on the screen. It's impossible to weed out those biases, but I think it's fun to see where the biases hold and when they get upended. Sometimes something really unexpected causes a major upset, and those are really entertaining (hello, stooge fandom!).
If this was a more formal study of boxart quality, perhaps I'd do some sort of experimental controls. Send out surveys to create a formal Boxart Evaluation Panel, require an analysis essay before voting, something like that. But then the biases directing the whole thing would be my own, and I don't want that! The fun of it is in seeing what tumblr thinks, warts and all. (And also I only have so much free time - sometimes I can barely keep up with the pace as it is, lol).
