The very point of all the blood and gore of animal sacrifice in the old testament was to stress the seriousness and solemnness of the occasion. I am certain that the sacrifice of animals, the gruesome scene, left a imprint on the mind of many a young boy and girl seeing such a thing, not to mention grown men and woman.
To those that say God had us killing animals then so why not now, it is clear that God originally did not want us killing animals, they are his creation. It was the sin of man who caused the entire world to fall. We took everything with us. We may have even possibly caused decay to enter the world, maybe even the universe. Remember, we were supposed to live forever.
So God told us to use the animals as a sacrifice. The life is in the blood. That was what was required, so serious is sin. Without God's grace, one sin is death to us.
Finally Jesus, His precious blood, was the ultimate sacrifice.
Which means, we have no more reason to kill animals, much less torture them. It is the new testament times we are living in. Comparing what happened in the OT is not a viable comparison.
Gen 1:29 says we were originally to eat a diet of vegetation. When we fell, God did not say start killing animals, only we would have to work the soil.
What we are doing to animals today is just yet another manifestation of our hardened hearts.