Why is it that I have to add "-reaction" to the search every time I look up a kpop song? Very rarely there might be a "my friends who don't know about kpop" one, which could perhaps offer a slight insight into where cultural perceptions presently stand (even though we all know what it will be unless maybe you're showing girl groups to guys), but most of them are someone recording themselves. Here are the reasons this practice is shit:
1] Nobody gives a shit how you reacted. Nobody knows who you are, you aren't even youtube famous or a live streamer or anything, so your feelings are not important to the general public. The only people who could possibly care are friends, who could just watch you react in person or on Skype or something.
2] That probably isn't your real reaction. You see, when you set up a camera to watch you react to something so that others can see it, that has a psychological effect that at best makes you self-conscious to hide things that you may perceive as unflattering, and at worst makes you fake react more obnoxiously than a JAV star getting her cooch stuffed.
3] The fact that a fake reaction is more likely because you set this up to record yourself stems from a larger issue: This is a practice of pure vanity done for attention and likes. That is not only groundless (Point 1) and disingenuous (Point 2) but obnoxious in it's own right. When you want to interject yourself into the public sphere (in this case, search results and recommendations) to take up people's time and attention and possibly even make a little money from it, you should be offering something meaningful like a review or commentary. This is not something meaningful because...
4] Reactions have nothing to do with genuine reception. The only thing they are good for is marketing evaluation to figure out if it's the kind of thing that makes people buzz to get your product attention. Every single time you react to something, it sinks in a bit more, and then you discover your true feelings about it. So these videos are not only an imposition of something that is and ought to be a more personal social experience, but it's a personal social experience that is only worthwhile for the emotional bond that the shared experience would inspire, as right afterward only the memory of that first contact with the material that is shared with others remains and then the true thoughts and feelings about the material develops. So you are literally trying to elevate to substantial meaning something that is really only worth the sentiment of a memory had it been shared with friends, which it was not.
So if you make these videos, care about them, and/or regularly interact with this phenomenon among the kpop fandom as if it matters at all, congratulations! You are participating in a completely meaningless, utter waste of time. You might be full of shit.