Went down the rabbit hole about medieval marginalia once, and a lot of it is essentially medieval meme culture. Some motifs appear over and over, so it could be an inside joke or cultural reference. Some of it is satire, or tongue in cheek commentary, there’s a lot that suggests subverting or inverting traditional roles. There’s a lot that feature butts and fart jokes. Most of what might have been at the root of it is lost, but yeah, it’s mostly humans being human.