I used to consider this kind of thing as 'kids these days' thing too, but when I actually started to watch reaction videos, I think I understand why. It's basically seeking validation on our own opinion, finding people who have the same passionate reaction to what you experience yourself and kinda spiritually bond over that. Even better when you have reactors who are genuine, entertaining, and/or insightful about the things they're reacting to.
It's actually something I really enjoy as an Old Person, because I have much less time and like-minded people to physically watch something together these days (especially with current situation...). Don't be too overly suspicious of this New Era stuff, you guys, just give it a shot and you may actually have some fun.