This is an interesting view point, I can’t say I have known guys that were jumping up for joy to have kids. I have no doubt there are guys like you have observed and seen (And not downplaying your experiences), but my anecdotal walk through life is more to attune that the female partner is like … how can I get him interested in actually having kids and putting in what is needed to build a nest/household for a two person relationship.
I have a horse farm and I see what it takes as the mares get older and the genetic issues, the aborted foals, the ones that you have to put down fast or last a few months and then have to be put down.
The sad reality (even if modern society and medicine down plays it) is that women have a small envelope for having low risk kids with minimal complications but the risk is always there, and as you point out … having another life in you grow and split off is very taxing on a human body.
So personally I get why women are very conservative when it comes to pregnancy since it is something that for 9 months will suck “everything” out of you, and then once born a consistent need and worry to maintain that life that can’t maintain itself.
Conversely, one wonders about large family fetish’s folks, that if they actually had to work in that framework like a single parent if they would still have it.
i.e. Watch what you wish for ….