To prevent it from being flagged as for mature audiences and potentially getting a strike on the channel. Showing fecal matter in high, up-close detail would mark it as a "V" rating (violence/disturbing)[0]:
> Examples include real or dramatized medical footage, or depictions of disgusting or scary content in a horror or fantasy context.
Youtube doesn't care about that. At least, content creators don't generally take that chance. There is very little recourse if Youtube decides your content violates their rules.
That was from the "mild" section, too. Looking at the more extreme bullet point for the same rating, there's
> It may also include pervasive imagery or situations that are disturbing or repulsive to the average viewer.
Which, given that the entire video is about literal buttholes and feces, probably fits to some degree.
A bit like for fair use in educational contexts, it can approved after a few (?) back and forth with the YouTube moderators, on a per video basis, if the creator is lucky enough to get reviewed by an actual human.
Otherwise the video just gets flagged and there's no recourse.
