Far more people than seems reasonable. There's a strong streak of desperation surrounding sex, especially the less common forms.
This particular orientation is one that can't be talked about in most public situations, and can be very very difficult to share with even a very trusted partner.
There are many among us who seem to think "everybody's gettin' some but me!" and use that as a justification for very bad behavior.
In places where farm animals are pastured, there's a seemingly easy opportunity. Thats why its called fencehopping. But it ought to be called "trespass with intent to commit animal cruelty" because most of these idiots haven't a clue.
They're quite likely to do damage to a critter requiring a Vet's attention, including surgical repairs.
It's immoral, it's cruel, and it's pretty stupid. Its even potentially deadly to the hopper.
If the Stallion, or the herd Bull or other large creature doesn't stomp the perp into the ground, the owner MAY decide to shoot him.
These cases make the papers sometimes, like the repeat Hopper up Seattle way, who kept raping a prize goat, causing her much damage. The owner got tired of the vet bills, and the poor nanny's bleating distress. The hopper climbed the fence one night, and the owner took out his kneecaps. Made the papers after that, for sure.
Even the well-known and oft-quoted "Mr Hands" case, 20 years ago +/-, was fencehopping. The enablers, who helped to cause a man's death, did not own the horses they were fooling with.
Wow.... who does that kinda stuff?
Sooooo, short answer? Entitled little punks.