All other NSMB games have this category, and even the origional has this category. Why is this not a category on these boards yet?

Low% in general on nsmb games isn't popular enough so that's why the category isn't on the boards.

But the category can be on the CE sheet managed by @Mchan338 if you do a run of it though. ( https://docs.google.com/spreadsheets/d/1G7C8So7I3_Nd11MNhbE_8NHk8s6FO8sf1WB8DbJx4Rc/edit?usp=sharing )

I dont think the boards for this game can even support any meme categories due to the way they are set up. Like romain said though, mchan has a category extensions sheet that they can go under.