If you want to pay the mortgage, have a fulfilling job, have time to spend with your family, and give your child a good start in life, you can't have 8 kids in a middle class family.
Sometimes 1 is the right number if you want your child to be successful and have enough free time to enjoy life yourself.
That IS resource constraint, the resource just isn't food.
The replacement rate is a little above 2 children in the modern world. Three kids is a burden for a lot of people.
My paternal grandfather was a farmer. He had 20 children who survived to adulthood. By two wives, the second having been the nursemaid. As I understand it, all of the children worked. Basically as soon as they could walk. Girls focused on childcare and housework, and boys on farm work. If they'd been living in a city, the boys would have had factory jobs.
So anyway, that's how you raise many children. That or be wealthy, of course. But current expectations, social norms, and laws make that impossible. Except perhaps for farm families, where substantial child labor remains legal.
"Freedom of career" for women is more like freedom to have to work. It's hard to raise a family on a single salary. Previously, a woman would work at home and husband would work outside. Now both of them have to work outside of the house to pay for appliances that do stuff back at home.
IMO one of the top issues is housing cost. Increasing specialisation, both parents having to work and urbanisation means people are crammed into more and more condensed cities. Space comes at expense. Children need space. Cheaper space out of the city means more transport costs and/or less job opportunities and likely lower wage. All in all, children is damn expensive.
People want to buy more stuff? Hardly a requirement of years gone by.
People want more free time? Doubtful, otherwise people would work less and buy less stuff - which we don't see. People keep getting more productive, but they just funnel that into a more expensive lifestyle rather than cutting back on work.
I don't think the reasons are simple (or even the same between people) but I don't think it's dominated by resource constraints.
I know software engineers with no children and school teachers with four. Very different lifestyles, but all middle class. And I don't think resource constraints factored heavily into their decision making.
Since both parents now work, often with lengthy commutes, there isn't a whole lot of person-hours left to spend with the children. That means people have fewer of them.
When the kids get older and it's time to send them to university, well, that's something which has gone backwards in affordability. The cost of a university degree has shot through the roof. How could anyone afford to send 3 kids to university these days, let alone 8?
Why do you say especially the woman? Not trying to pick a fight, I'm genuinely curious.
Kids have turned from a resource like they were to farm families to an expense and an increasing one at that - and I don't mean in a "kids these days" sort of way - the world changed and not people. Which leaves children to be had by those who want to have them for the sake of having them - some sort of enjoyment or sense of obligation.
1. Backup in case things go wrong (meteor strike, end of the Earth, nuclear war, mass plague, AI/robot revolt)
2. Outright inability to live alongside other cultures and societies/groups. Just like throughout history, some beliefs will also be controversial at best/illegal at worst, and while in the past finding a unoccupied area on Earth was practical, that's not really the case now. So space it is.
3. Science/academic study. Robots are neat, but there are some things it's better to send humans for, and a fair few scientists would probably rather be out there exploring than sat behind a computer screen.
4. General boredom/tourism/whatever.
5. Environmental concerns. Not just resource mining, but let's face it... eventually a lot of environmentally unfriendly industrial processes will probably work better in a place with no atmosphere/biosphere to ruin.
Probably a bunch of other things too.
Population might just stabilize at some point, and then there's not much of a driver to expand off of our planet (apart from some resource mining, and other activities.)