Hot take: Meme review works not because of the memes, but because it is cute/funny to see the reaction of the jp girls to western culture. And while there were some girls versed in meme culture (Polka and Miko), it makes sense to use "normalfag" memes from reddit because most of the guests don't know that much about western meme culture, either because of the language barrier or the lack of research on the subject. Try to imagine Coco having to explain the rrat meme to some one like Subaru. It just wouldn't work without lots of exposure to western memes beforehand.
>Tl;dr
Reddit is a necessary evil for the Meme Review formula so it is interesting for the guests and the viewers at the same time.