Looking at your question, there are a few problems with it that caused it to get closed.
It's Too Broad
From the help center on things you should not ask one item states that any question where "every answer is equally valid" is not a good one. Asking people to share why they had kids falls under that in my opinion. Every answer is going to be a little different (though there may be some common themes, just about any answer is a valid one). That makes it into a polling question, which is also discouraged. Someone defined "too broad" once (apologies that I can't find it right now) as "if you could imagine a book on the subject, it's too broad. If you could imagine hundreds of valid answers, it's too broad". Your question fits the latter part of that definition.
The Presentation Needs Work
First, it's a bit hard to read. Some parts don't really flow well and it feels like there are little bits missing. I had to read it a couple times over and there are still parts where I'm not quite sure what point you are trying to make. Hard to read questions are less likely to be interpreted the way you intended them to be.
Second, your tone and the way you address the audience. You are on a parenting site, so most people here are going to be parents (or in a parenting-like role). Your question could easily feel condescending towards that audience. Your question reads like this "Science (and other arguments) show that having children doesn't make rational sense. Why do you people do irrational things like having kids?" That tone (whether intended or not) isn't going to win over anyone in your target audience. Hence many of the downvotes.
Additionally, your edit changes the way the question is viewed. Ignoring all the previously stated problems, you might have had an interesting and sincere question. It is a lot easier for people to want to answer a question when the asker appears to genuinely want to get an answer. But your edit makes the question appear very insincere. I would hazard a guess that many people, were they to answer, would say they have kids because they bring them happiness. That edit is very dismissive and argumentative towards that answer (which is a valid one for some people). And that makes your question feel like a "rant". It feels no longer like a question, but a way to argue with people as to why they are wrong for having kids (again, I don't know if this was intentional, but it comes off that way). At that point, it isn't a question and no longer belongs on a Q&A site.
One Size Does Not Fit All
You've cited other (somewhat) similar questions that have been accepted on other SE sites (namely this question on Health.SE). There is a problem with pointing out questions on other sites as evidence that yours should stand, specifically that the communities are different. What one SE community will tolerate in terms of broadness, subjectivity, etc. varies widely. For example, a site like Parenting allows questions with a fair amount of subjectivity. It's just the nature of the topic. But on a site like StackOverflow, you would be well advised to not even intimate using a subjective word like "better" or "best". That causes questions there to be closed with ludicrous speed. So just because such a question survived on Health does not meant it works here.
If you had found such a question on Parenting, you would have a more compelling argument. Finding such a question would prompt re-evaluating both questions. We may keep yours, we may close the existing one. It depends on how the site rules and it's community have evolved over time.