Notice that most of the comments here are describing post-hoc how having children has been fulfilling/great/worth it. Which isn't really the question - it's not asking if having children was a good move in retrospect.

It's interesting that most people's minds go there. I've had this happen myself after having a son - the original "why" almost doesn't matter or rather gets overshadowed by all the other parts of it (for most people, a deep sense of purpose and fulfillment).

To actually answer the question, my partner and I came to a place where our relationship was great, jobs were great, etc - but we felt a certain "is this it?". Sure, being DINKS is a nice life, lots of travel, easy, etc. But... hmmmmmm... is this it? Amuse ourselves until we die? Stay clean and simple, have fun, work hard... hmmmmmm....

Meanwhile there was a quiet impulse in the background beckoning towards creating something out of our relationship / position. It's hard to describe. Obviously biology is playing a role here. But what a wonderful chaotic creative thing, two different people coming together and making a third person.

So we had a vague sense of all that. And decided to go for it. As many other people have said in this thread, your life changes immediately and irrevocably when kids arrive, but for us it's been pure joy. Lots of chaos too.

My wife remarks that she didn't realize what a big hole was in her life before becoming a mother. That's maybe the best way to describe it. We had a sense that there was a hole in our lives, or something that would grow into a big hole if we didn't have kids.