cruelty to animals

I read recently some explanations of the prohibition of yoking an ox and a donkey together when plowing. The reason, cruelty to animals. The donkey will see the ox chewing its cud and be jealous that the ox appears to be eating. Another reason, they have different strengths. One will overwork the other. Another reason, each creature likes to be with its own kind. I can't recall where I read this but the commentary was from the Chinuch and other such sources.

I immediately thought, if we are to show humanity to animals why in my BT yeshiva did they treat us so horribly? It's been nearly 40 years. Still, that's what came to mind.