Why? Did you get stuck in a washing machine yourself at some point?

On a more serious note, I remember reading an article once about this phenomenon. About how it's not some widespread latent sex fantasy to fuck step-siblings. Rather it's an odd reflection of how algorithms poison the content in this attention economy. The more unusual the content is (without being outright objectionable), then the more attention it gets for being so unusual. That starts a wave of new creations from content creators to jump on the bandwagon for the popularity of the content that seems to be getting traction. Then pretty soon anyone not catering to this "demand" is an outlier and loses out, so eventually this theme of content floods the entire ecosystem.