Probably because a lot of it is real fucked up, and makes people uncomfortable.
Like female bedbugs not having vaginas and so males have a sharp penis and literally stab the females with it often resulting in death of the female, because it’s literally just an open wound.
Further, male angler fish only exist to find the female, touch her, get stuck to her, and get absorbed by her body until all that’s left is the testes, now absorbed by and part of the female. The female can hold multiple testes of multiple males inside of her and choose to self-impregnate whenever she chooses.
Don’t even get me started on felines and spiny penises so the female can’t escape once the male has entered.
Like a huge amount of animal sex is rape.
Yeah I don’t spend my time reporting it because all it does is remind me how lucky I am to be human and be able to have a consensual, loving relationship with another human.