Usually, it's bc some anon gets caught, and the prosecutor finds out there is no law specifically against bestiality, so he calls his legislator who advances a bill that is an easy slam-dunk- who would vote against a bill outlawing bestiality? Who?
Nearly every normie thinks it's horrible, we're horrible, and they *hate* us even though they don't know we're secretly their bosses, best friends, wives, sons and daughters, etc.
So the law is swiftly passed with zero questions or opposition.
No debate. Not: Do we need this? Isn't there existing cruelty legislation that covers harm to an animal? No, none of that. Anything involving pleasure is outlawed, why, just because. Well, they say, animals can't consent. Sure. Go try to fuck a mare that isn't in the mood, fella. I'll visit you in the hospital.
Then they have to carve out some language to make actual animal abuse ok, as long as it is couched in the guise of "animal husbandry" i.e. farming. It's perfectly ok to forcibly shove your whole arm up a cow's ass or vagina as long as it's for "farming" purposes. Or to place an animal in a truss so they can't move while you inject sperm through their abdomen directly into their uterus with a giant syringe. Perfectly ok, yep.
But don't get on a stool and get your penis into that cow, man. Then it (gasp) is about pleasure for both parties. Why, that ought to be illegal! (law passes)
In the eyes of most, just getting a penis or vagina near a dog is harmful to the dog. People think sexually mature animals are "babees" or come from Disney with no genitals nor sexual urges and needs. They want them that way. If they could turn them into animated stuffed animals with no hint of genitals or anus they would do so in a second. Why do you think "fixing" is so popular? Removes (uncomfortable!) mentions of sex and desire from their squeaky-clean ideal of a "pet" i.e. animated stuffed animal- all love but no slimy bits.
People are dumb and I dislike most of them. Zoo is the ultimate cheat code. I can get all the love and sex any man could want and I don't have to deal with people and the games and bullshit. They may think I'm stooping to a "lower level" but they're mistaken. I am elevated far above the madding crowds of filthy unthinking humanity. Where I stand in my quiet circle of love, respect, and affection with my companions, I am free of all of them.