Yes, because they are the same as us - humans.

Animals are not necessarily subhuman, but clearly not human.

I mean, I guess I could go into detail about the differences about the behavioir of animals and humans and what that tells about their intelligence and inner life, but I am not such a big fan of typing to be honest. I will only say that animal behaviour is simple enough to be predicted, ehy always act on the strongest impulse: whether it is food, sleep or whatever. But a human has a such complex network of character, desires, affect, beliefs, and emotions, that they can in a way that is impossible to predict. Can you imagine an animal starving itself to death deliberately? No, it would not be able to do that, as it's instincts would overpower anything else if it got sufficiently hungry. But we can have other reasons for that that we act upon.

Honestly, if I was a vegan, I would almost certainly not say thay animals are as complex as humans, as most people would probably(quite rightly) not agree. They are more primitive as a great deal of what makes us us is our complex social structures that no animal has(even highly social ones). We have meanings and values given to us by society, which animals do not have. We are capable of morality, animals are not. I am honestly tired of typing. I think the point is clear enough now that I can stop.