I’m inclined to believe it’s one of those things that, once it enters the recommendation sphere on your account, it’s really hard to get it to go away without manually removing profiling info via Google account settings. I just remembered now, at one point he did run a personal experiment to try and see how extreme the content would get if he let it play after it started showing up. After getting kind of disturbed with how bad it got, and bored of laughing at it for amusement, he tried training the algorithm to only show him cat videos and kind of settled on where it currently is. I’m guessing his account has a lot of those older associations still tied, and the algorithm tries to rekindle them from time to time.