RebYidd23,
Animals don’t lock up animals in cramped space and deny them proper food and companionship. People do.
Cats torment mice and birds. Feivel can tell you about a wasp that takes over the brain of a spider and drives it around before eating it alive. Dogs sometimes shun other dogs at the dog park.
By acting like a plant, a human being confines his neshama, keeping it from rising, deprives it of companionship with Hashem, and fails to keep it fed via spiritual growth. That doesn’t make plants evil or make it an insult to call a person a plant.
To willfully act like a plant would be evil; however, we tend to be more repulsed by active evil, e.g., harming others. And the vast majority of plants are not active.
The sins for which people are called “animals” are not of the types of actions that animals do. They are of the exclusively human evil variety.
The exclusive human evil variety is a toxic gumbo of animal impulses and human intellect.