I believe Netflix has talked about thumbnail experimentation at length in some of their engineering blogs [1]. To me, it seems perhaps Netflix has figured out a running theme in the author's viewing habits... perhaps the scandalous, soapy stuff is what they keep clicking. Same kind of reaction I get when a guy friend tells me they keep getting ads for women's bikinis or women's underwear in their Instagram ads. It is…
No, that "gotcha" is blatantly wrong. If you follow running people, Instagram will float you popular running content. What's popular running content? Girls posing in yogapants. Same for other niches. The most popular and thus shown content will always be a sexual version of the theme.