Same reason why I am absolutely terrified of playing any instrumental music on Spotify. I let one track run till the end and my next 2-3 discover weeklies will be filled only by instrumental music.
i used to instinctively turn on private mode every time i opened the spotify app (on desktop at least, since it was easy enough to get at)
with youtube i usually open a video in a incognito tab anytime im watching something random, otherwise it takes weeks of clicking "not interested" just to get rid of some recommendations. sad times
I have the same experience with vocal music on YouTube Music, funnily enough. I greatly prefer instrumental music but you listen to one vocal album and suddenly all they recommend is singing.
You can use this behavior to your advantage though. I have my browsers set up to delete cookies when they are closed and from the surface this works for Youtube recommendations. If I open the site I only get very generic popular/pushed content.
So after I watch that instrumental music video, there will be a mass recommendation for other instrumental music. And that's nice, because I apparently was in a mood for that. And the next day, I open my browser again and they are all gone! I can dive into the music for the mood of that moment right away.
with youtube i usually open a video in a incognito tab anytime im watching something random, otherwise it takes weeks of clicking "not interested" just to get rid of some recommendations. sad times