As someone who enjoys both kpop and western pop I feel there's definitely something that about kpop that creates a more intense fandom, but it's not easy to put one's finger on why exactly. One reason might be that in the western music industry there's more of an assumption that the product is the music whereas in kpop the artist is the product. Kpop artists put out a lot of material that makes you feel close to them and makes them relatable. I'd say that the culture of Korean media is more intimate in general. Kpop stars appear on a lot of tv shows where they just play games, share stories, spend time with at their home, work, coffee shop, restaurant. If you have a favorite western pop star you might see them on a talk show or read their Twitter feed, but it doesn't really feel like you're spending personal time with them week after week.