Because unfortunately most families do what makes most economic sense.
DH had worked P/T due to studies many years ago and the reality was that he ended up doing 95% of his job on 80% pay. His salary was over double mine.
He used his niche skill set and ended up in a well paid, STEM career. At that time he was earning over double what I could earn by teaching on similar hours. The cost of him earning well is travel and some unpredictability. Something had to give because the pair of us working 100+ hours a week without support was not sustainable for our family. So it was my job.
In the absence of affordable, autism-friendly childcare, stepping back from my career was the most pragmatic move.
The shift from this needs to be better access to shared parental leave (when I hear families doing this I know which company the dad works for) and shifts in employment structure and salaries.
Losing £££,£££ over the years by putting my career first over his would only have penalised us and not changed the world.
However when I was working, if he was in the office, he was first contact for ill children as he was more flexible for that. Not much help if he was hundreds of miles away or in another country though.
If I go back to working 50+ hours a week as I was, that's a hell of a lot more unmonitored time for my teenage son on the internet...
I could get a less demanding job... for "pin money"... but that's not helping the feminist/ healthy mascilinity cause much either.
Basically I cocked up my life choices by not being born to parents of optimal demographic for free childcare and not having the interest and talent to get paid well in the STEM sector 🤷♀️