ngl i was confused i thought you were talking about politics from the title - and then i saw the section this was in lmao
i'd argue it's because a certain section of fans like to see growth in their faves. they don't necessarily want perfect gods who have swooped down from the heavens to save kpop, they want people who they can relate to, and feel proud of over time. ofc not everyone has "potential" in their eyes; only those with a love for performing onstage along with a terrific work ethic and a genuine wish to improve do.
@Selfmate took dahyun as an example for someone with potential, and i wholeheartedly agree with his point (though do note i'm a dahyun biased once, so i may or may not be biased...). dahyun wasn't the best singer rapper or dancer on sixteen, nor is she the best singer dancer or rapper in twice. but she's improved leaps and bounds due to the factors i stated above: love for performing, great work ethic, wish to improve.
taking dahyun herself to substantiate my next point, i'd also like to add that certain people just have an innate talent in things that are not performance related and thus they debut as idols. you know, say, variety skills. this is extremely important for a idol cause that's one of the things that set them apart from musicians in other genres. idols can be jacks of all the performance-related trades (or even worse in them) and masters in none of them - in fact that really is the expectation. but by proving themselves as fun and engaging variety personalities, idols can gain fans. this is another reason why dahyun made it into twice: she has the variety skills (i'd take this further to argue that jiwon, who is now in fromis, realised this and upped her variety game by leaps and bounds, which is what got her into fromis. in terms of talent, why, she could be twice's second main vocal. but on sixteen she hadn't yet come out of her shell. by idol school, she had). so someone who is exceptionally skilled at variety, loves performing onstage, has a great work ethic and a genuine wish to improve themself... most certainly has potential!
besides, some idols may have talent in one aspect of their performance, but may not in other aspects. to watch them improve by leaps and bounds in those other aspects is a great feeling for a fan, and proves that they had that potential all along. the biggest example i can think of right now is shinee's taemin. right from debut one could tell he was a great dancer, but it is only over the course of his career that he has been able to improve his vocal skills, going from a sub-vocal position to a lead vocal position, second only really to vocal gods onew and jonghyun.
so yeah the end of my long essay on why some people vote the way they do. that said, i haven't ever voted for a kpop survival show, and if i were to, i'd consider a variety of factors besides "potential", with a heavy emphasis on whatever skills they already have (though factors like general likeability, variety skills, and yes potential, would definitely be considered).