It's no wonder that "gamification" was such a buzzword a couple years ago. Simple clicker/tapper games were just getting mainstream coverage, and every bored pleb on Facebook was playing some 'ville derivative. But what is that hook? I for one don't think it's a visual cue. Is it the act of rewarding skilled play? Perhaps, but the variables of "what makes skilled gameplay" and "what is a reward" are nebulous and distinct for each gameplay experience. The umbrella answers to each are 1) quick completion and 2) items used in games. 2 seems to be a major factor here. Rewarding players for watching ads is the new hot garbage, with companies offering these services springing up every quarter for venture funding.
Maybe I just don't want to believe it; as little faith as I have in humanity, I still want to believe you need more than shiny trinkets to gain favor with the masses. Deep down, I know that's wrong, but like the X-Files, I want to believe.