The backend on YouTube is pretty much designed to encourage skub (ragebait/“engagement”). Having comments that are incendiary is good for the video’s performance.

Does that make it the perfect breeding ground for astroturfing and pushing misinformation? Probably. Bad actors can basically use it as a cheap form of advertising and pushing ideas that benefit them. Even the creator of the video if it was a video that has a completely opposite viewpoint of those comments still stands to benefit from having them because that increases engagement and their revenue.

So I guess my point is is that YouTube has a lot of problems and there is a multitude of reasons why comments like that have a home there and motives for them.