Typically when women have kids they realize that raising their offspring is more important than maximizing their earnings. I’m sure many would prefer to quit altogether, but many still have to work to make ends meet. On the balance, men don’t care as much about raising kids and they also derive more self-worth from work.
I'm a woman and it's correct as a data point though their assumptions about how the women feel about it are less accurate. In most cases, the male earns more and/or it would be a bigger hit to his career to be the primary caregiver, so from a household composed of a het couple and their kids perspective it makes sense for her to be the primary caregiver.
Usually someone has to step back/make compromises once children are had, because even good childcare won't take your kid if they're sick, and things like pandemic/staffing school shutdowns can leave people without childcare. For example, my boss's kid's school just shut down 3 hours early because too many of their staff were out sick. So the parents were just kind of stuck.
Silly question, and I hope you don't mind, but Feet, about how old are you? I'm curious, that's all.
At some point in your life, things like these will be "of course" to you. (Eg women more often wanting to be with their kids, or choosing jobs where they get to take care of others. And men, looking at large numbers, caring less, and more about themselves. För evolutionary reasons...).
I'd be wary of assuming the women's (and men's) choices are evolutionary - or at least nature versus nurture. It needs to be remembered both that having a choice at all is a fairly recent decision - 99.99+% of humans who ever lived didn't really get to 'choose' in the way we do now - and that choices are really hard to separate from societies in which we live.
When you live in a small group like most humans, you do what needs doing because if you don't, it doesn't get done. Think a nuclear family unit: If mom is out of the house, of course dad changes the diaper because otherwise it doesn't get changed. But all the time. There are some tasks that only can be done by one sex, but very few. Turning down a competent hunter or caregiver because they had the wrong genitals is suboptimal for group survival. Overspecialization in general is only possible after a certain number threshold has been reached.
The social part is important because it's also important to remember that evolutionary history =/= written history. We don't have records from most human societies. Limiting our data set to written records on gender/sex cuts out all pre-literate societies and also introduces substantial bias. (e.g. just because cuniform exists doesn't mean that any average person can use it or that their writing would survive or be accurate).
Modern societies have, up until recently, been fairly restrictive on the basis of sex. My mother wasn't allowed to go to college and her interest in electronics wasn't acceptable. This in turn impacts what I (and my sister) were told: Most parents will give their children advice that they think will help the children survive and flourish, so girls are told to lean in to their communication skills while boys are told to lean in to other things (I'm not a boy, I'm not going to speak on y'all's experience). Likewise, I've heard from men that a fair amount of them had to discard the part of them that would want to care for others/go into a caring profession.
There's also how we categorize professions as caring or not. Doctors vs. nurses are a good example as are college professors vs. high school teachers. A high school AP Calc teacher is in a 'caring' profession, but an adjunct teaching algebra in a community college is not.
And that's without even getting into 'is the average human aware of why they make choices'? The majority of what I've been told/seen has suggested that the couples make the decisions on the basis of finances, but I don't know if that's true or if it's just the most comfortable story for everybody. Humans are great at lying to ourselves, particularly if it helps us fit into a group.
Take a look at Scandinavian countries that have the highest levels of gender equality. When women are given the most freedom, they choose to spend more time raising children than men, and they choose less demanding jobs than men. Women and men have overlapping interests but women tend towards children.
This is the scientific answer. The 'hey, im old now answer' is from life. Most of the women I worked with have exited (80% not in tech nor working), and the women in my friends group are raising kids rather than some shit job.
You might want to take a look at the cost of Kindergarten or similar care. People I know (in Germany though) made this calculation: to work and pay what I earn for Kindergarten or one of us does not work and takes care of the kids.
But TLDR, whether by preference, or because there's no better choice, much of the gender wage gap can be attributed to the fact that women are usually the primary caretaker when kids come along. Part-time roles can be a good way to give women (but really any parent) more options on how to balance career and family. At least in the US tech industry, often times the answer is really work or quit without many intermediary options (that are well known at least).