Humans want to have authority over someone or something. We are genetically pre-programmed for that.

In the past, we had authority over our tribes, families, and children. But nowadays, people have become so weak and unintelligent that most can't create communities. Some are afraid even of creating families.

Also, to have authority over others, you need to be smarter, wiser, and more competent, which modern humans lack.

So, instead of leveling up to fulfill our evolutionary roles, we adopt a pet — a useless, unintelligent, all-obedient, always-loving creature which allows us to feel that authority no matter what.