If women want a career then they basically have to leave their children in the care of a stranger all day, and miss important bonding time with them. Many chose to care for their own children rather than work their guts out to pay a stranger to do it and then still get hassled by pressure from their manager to not take time off when their child is sick and the child minder won't have them until they are well again.
Working on the railway? Try getting childcare beween 21:00 and 06:00! That rules out most turns of duty for train drivers as you'd leave for work before six for earlies, and get home after 9pm on lates.
If you looked at pay discrepancy between single Dads/Widowers with children, maybe you'd find similar results in that progress in a career would be slowed, or reduced hours and therefore pay would have been sought.
I knew a Driver who was a Widower with children who was accommodated to work only Monday to Thursday on mornings after 07:00. However, he was obviously able to come to an agreement with a family member to care for his children all day on a Friday or Saturday as he worked his rest day quite often outside his regular times. He was probably trying to manage a challenging situation and needed the money just like many Drivers do, and it didn't bother me, but there was massive resentment amongst some that the more sociable shift was unavailable to the rest of us Monday to Thursday, yet he could do anything on his (regular) Friday and Saturday rest days. The resentment was to such an extent that someone 'keyed' his car!
I think you'll find that the Primary Carer of children generally have lower earning potential, and that most of the time this is women.