My first child is due in 32 days. So, I'm excited to see how this parenthood thing works.
We made the kid on purpose. But, I can't say that there was any deep thought that went into deciding to have a kid. when I was younger, I always assumed I would have a few kids. I just figured it would be a good experience. But, as I got into my mid-thirties and hadn't had any, I started to consider the possibility that it might not happen. That was tough to accept it first, but then I came around. I figured if it happens, it happens.
I got married 4 years ago. My wife also was interested in having kids. So, about 3 years ago we started trying. After two years we had no success, and I again started to consider the possibility that kids would not happen for us. Then, the wife gave me the good news, and the focus change for making a kid to successfully bringing him into the world. It looks like that's pretty much certainly going to happen, so the focus is changing now to keeping this kid healthy, so that we can then focus on making him a success. (My definition of success is extremely broad, so let's not get into that part.)
anyway, my underlying point here is that there doesn't necessarily have to be any big deep reason for it. Sometimes it happens by accident, sometimes it's a thing that people do just because they think they're supposed to do. Other times it's done on a whim, and still other times entails much frustration and heartache. it's a basic biological function, and it's necessary for survival of the human species. And ultimately, whether we consciously think about it or not, that's the purpose.