I think a large part of it is people mindlessly clicking on and watching low-quality, clickbait, garbage content videos, combined with Youtube's algo aggressively assuming it's their new favorite thing and thus flooding their suggestions with that topic. The other issue is that it is possible to tune your suggestions and tell Youtube you're not interested on a suggestion, but people don't know how to do that, or they feel it's too time consuming to weed out the bad suggestions.