Specifically, they are trying to (a) spam you with Netflix options to find some Netflix content that you will get hooked on so you stop looking for non-Netflix

Specifically, they are trying to (a) spam you with Netflix options to find some Netflix content that you will get hooked on so you stop looking for non-Netflix content, and (b) give you the appearance of inifinite available content by making the content you haven't watched look different every time you see the cover image. The mistake is in breaking the illusion by also rotating the cover look of content you've already watched.