If I recall correctly, ever since videos could be called up as ads you can just pay for any video to be an ad, as long as it's on YouTube, and it doesn't have to be yours. I don't know if this has changed, but an essays channel figured out that that's the fastests way someone could target a competitor's channel. Paying to have someone else's video as an ad tanks that video ad revenue and discoverability instantly. Ad views count as views to the video and skipping an ad counts as a skip on the video which signals the algorithm to think that nobody wants or likes to see that video. Do it to enough new videos and you can entirely kill a previously profitable channel in a couple of months.