I think what makes Kpop one of a kind is just its way of popularizing idols. Korea literally has hundreds of idols, and the fact that us fans can keep track of a large majority of them because we care about them is incredible. Kpop is really good at introducing new talent and letting fans "come to groups" and test out the waters to see if they like them or not. A group will release a song, set up a few SNS accounts, maybe have an introduction video on their own show or a V app stream. Then the fans come to them.

Because the entertainment industry in Korea is so closely related, there are lot of platforms through which Kpop reaches an audience and lets their fans get to know the groups on a more personal level. Like, there are people who can sort SNSD in order of height. How do we even get that kind of information to be able to do that?

The constant exposure of media that idols get is much more than any American artist, but it's because of this that we grow to have a more personal relationship, biases, and care about these otherwise ordinary people.

Lastly, although the term "idol" literally means someone you look up to, I think a really unique thing about Kpop is showing vulnerability. These idols are super young. They're people, too. You see them smile and laugh, but you also see them cry and be hurt. The reality programs that show that a group of six or seven guys and girls living in a relatively small apartment, and getting up at 5 AM to prepare for a 19-hour day, add a layer of reality that we don't get from seeing Taylor Swift on TV.

TL;DR: Kpop is really good at making people popular and likable. We relate to idols a lot more than we do to anyone in American mainstream.