There's no logic in to thinking that they're not. Like I've said a few pages ago, why would anyone want to watch the original source when they've already seen it on the "reaction" video? I'm not just talking about trailers and commercials or news reports, I'm talking about animations (where animators really struggle trying to make videos for little reward in the first place), comedy sketches, and movie/tv reviews.
Sure, you can argue that these people put the link of the original video in the description below (assuming you have seen any of the people listed in the video in the OP). But lets be realistic, who even reads those? And how many if there are people who do? That's impossible to find out.... unless you read youtube comments. Sure, there's a whole bunch of toxicity to behold down there so you may not want stick your head there, but if you do you'll see there are a bunch of uninformed assholes there posting shit that is contradictory (even outright ignorant) to what is explained in the description.