Aren't users mostly forming parasocial relationships with "creators" and consider them friends, and want to be with those friends, regardless what they'll do?
I never understood the reaction videos and found them boring and stupid, if I wanted to have an idiot constantly pause the video and say something dumb that shows they didn't understand it, I'd watch it together with my 15yo self. But when I read discussions about it, users commented that they like it because it's something they can do "with" the content creator and they'll get signals to what their famous friend thinks about some topic etc.