It's a part of human nature that will be very difficult to ever get rid of. I think there's something instinctual, deep down inside all of us, that is capable of or enjoys seeing brutality or cruelty. We're more than capable of doing it to each other if the right conditions are met, look at the Yugoslav war, or other conflicts going on in the world right now.
Compound that ability, with alot of the world seeing animals as entirely "lesser" and therefore not worthy of moral consideration.
I know in central and eastern Europe, particularly in the rural areas, but I've seen it in towns and cities also, dogs are not seen as part of the family, or even pets, they are tools. They live their entire lives outside, they are shown very little affection or interacted with, I know some who spend their entire lives on 10' chains staked into the ground, just there to alert the household if someone comes onto their property. As an English person, this really offended and angered me, but it's the way life is. I know people in turn, who are very uncomfortable with the fact our dog lives inside, is allowed on the sofa, and is allowed to run around freely, as the concept of it is so strange.
I've seen footage from a Chinese fishing market, where a whale shark is being cut up and sold from the tail upwards, whilst it's still alive.
This isn't to say that everyone from culture x,y or z is like that, or that everyone from Britain loves and cares for animals, simply that different places have different culturally acceptable standards.
We won't be able to simply legislate this thinking away, particularly in places where people's lives are a day to to day struggle.