I'm using common sense, which is not so difficult as it looks on TV.
The purpose of businesses is to grow and make money. To expand markets and increase market share.
On the basis of this presumptive allegation, I hold that the propietors of the barnyard sex sites want to expand markets and increase market share.
Understanding the little-known phenomenon that pornography provides material for the sexual fantasies of it's consumers, and that these consumers like to indulge these fantasies, I've taken the wild leap in guessing that at some portion of this expanding customer base would like to actually engage in the fantasized behavior portrayed in their pornography.
However, bestiality is Illegal, so I've pulled the notion from thin air that people who want to get it on with a dog might not want to be arrested for it. An efficient way of insuring that would be to get a court ruling against laws prohibiting bestiality.
Then I got some tea leaves, and came up with the wild idea that people with bestiality fantasies might want bestiality to be legalized.
But hold the phone, because I'm working without a net, here. Here's a crazy thought: people who engage in one sort of sexual deviancy will be encouraged by the open-ended legitimization of another.
Dig it, baby. If it feels good, hump it. Anyone who says otherwise is a uptight, fundie bigot.
How can you be so sure they're not simply aficianados who like to trade their wares? Ask any cop who works on kiddie porn cases. Nearly all of it is freely traded by aficianados.