With 7.5 BILLION & increasing on the planet, humans are a "virus with shoes" to quote Bill Hicks. We have tipped the planet into another abyss. Poor parenting has left me with disastrous role models which I will not repeat thus saving the world more grief. Of my immediate family,m I AM the successful one as I reject their road map for life. Making their failed system work is not within the realm of possibility. No kids. No problem.

who in their right mind would want to bring innocent helpless human beings into this fcked up world?
had i to do it over again, i wouldn't.

Out idiocracy movie educated people have few or no kids trailer park have many not good gene pool dropping to ankle deep explains a bit about trumpers rise

Check

My sister and I both decided early in our lives that we did not want children. We came to our decisions independently. My brother had three kids and loved kids from the time he was a small boy.

My sister is religious; my brother and I are not...my sister and I have graduate degrees; my brother has a GED.

I think many factors play into this decision...does knowing the reason why you decided not to have kids change anything? Just curious...?

Every bit of your own nature/nurture combination is up for debate. But...with all 3 of you having no interest...I'd be more likely to bet it's more along the lines of more weighted towards one side of the nature/nurture...but there'd be no way to know, unfortunately, ever!

For instance...an example from each side:

If evolution's responsibility is to instill within us a drive to procreate (of which I have no drive either), perhaps their is some weird mutation that can occur which is intended to stop certain lines of genetics if that mutation occurs...

or perhaps despite having what you call a not rough or traumatic childhood, you were still implicitly shown that children weren't prized. This explanation might border on the "similar experiences" option, but, after all, "similar experiences" is a synonym of "nurture".

And those are only two of the infinite possibilities, though my examples are intentionally skewed to opposite, partly ludicrous sides... but... grand scheme... we are all an interesting confluence of nature and nurture... and one has real trouble untangling the two, because it could only be done by experiment, and those experiments would never be accepted as ethical.

So...while the question is infinite fun to ponder, I encourage you not to ever fully hang your hat on one specific explanation, to marvel at human diversity, and to enjoy your own unique mix!