It's not just because it's dogs, it's because the method of torturous death is some of the sickest, evil shit most people have ever heard of. Would it be worse if they did the same to humans? Absolutely. I think even the most rabid leftist would say the same. They are going to get away with it and probably continue because it's just dogs.
Many couldn't be bothered to even watch it. We've all seen the footage dozens of time, but the average leftist couldn't be bothered doing 1 minute of research on their own.