Sorry but anyone who says "out of the pool of mothers I know, the fact that they choose to stay home with kids proves that there is a significant biological urge to do this for the female sex class as a whole" must be deliberately ignoring the bigger picture (and doesn't care about actual, measured data).
Culturally and historically speaking it's only been the blink of an eye since contraception allowed women to have more control over family planning, since women were even conceived of having equal skills and potential in the workplace as men, and the legal allowances to work towards equality on this (parental leave, etc). It takes generations for changes, attitudes and opportunities to change.
In most cases it's a simple result of finances.
In my own experience I took time off/ reduced role because my work commanded far less pay and was more flexible than DH's (flexibility has improved a bit for both of us since Covid) AND I felt an overwhelming amount of guilt thinking about other childcare - mainly from comments on MN etc. There is of course a biological aspect if you breastfeed but that doesn't apply as a blanket rule to all women and all situations.
I know couples where they took shared parental leave, which is great if it works out financially. Within the home my DH does equal shares of "parenting" including all bedtime, lots of school run, getting bags ready etc. It's actually positive imo that he as a senior person in a private sector company is seen to do this (have flexibility around kids).