Why do people treat dogs differently than humans?

Obvious/sarcastic answer: Because dogs aren’t humans.
I’m not saying that we need to buy things for dogs that we would buy for kids, or spend as much time with dogs as we would other humans- I’m referring to respect and love here.

I just saw a video that talked about a nice lady who would take dogs in who aren’t loved anymore. These dogs are old and sick and/or possibly about to die. If a person’s mom was old and sick, they wouldn’t stop loving her. If someone’s mom was about to die, they’d probably want to spend the last few days with them, not give them away to someone else to spend the last days with them.

People do things to dogs that they wouldn’t do to humans. People would adopt a dog, then, for no reason at all, decide they don’t want it and give it back. You can’t adopt a human child and decide you don’t want it and give it back. So, why do it to a dog? This isn’t including people who adopt a dog, and then can no longer afford it or aren’t taking care of the dog.

Why do people treat dogs with less respect than they’d treat another person?