For an appallingly large number of people, getting pets is a choice, while having children is not.

One of the earliest books (1971) to explore being child-free was The Baby Trap by Ellen Peck. In it, she explains studies which indicate oldest-born daughters who shoulder a lot of the care of their younger siblings have a greatly increased chance of not raising a family of their own. Generations ago this was only more exaggerated, as boys mowed the lawn and took out the trash, while girls did everything else. This unequal division of labor extended to women who very much wanted to raise a family; only to discover they are basically doing it all by themselves.

I see engaged and interested fathers all around me now, and that's a great thing. Considering the acres of ink about how badly both girls and boys do with a neglectful and disinterested parent of any sex. In fact, it led to a spate of books at the turn of this century where women declared that getting divorced gave them more free time. Because they had ditched their "most immature child" who would never properly contribute and needed continuous care even as their own children took on more and more responsibility around the home.

Imagine you didn't want a dog but through family pressure, societal expectations, or "just not thinking about it" you got one. And you don't like it. This is not going to be a happy dog, or a happy person. Instead of enjoying the walk, the training, the expense, it's all a huge burden.

That's too many actual parents.