The mother being treated/expected to be more of a parent does not start at divorce. That's simply the continuation of a societal expectation that women will do the 'mothering.'
Because that social expectation is there, it is far more often true that in a hetro marriage the wife will be the one who gives up their career path to take care of a child. Thus the court systems has standardized on an expectation that the mother will need spousal support, and child support in a divorce, because she is the one who'll need to retool and rejoin the workforce, while still _doing_ the parenting she did while in the marriage.
Because that social expectation is there, it is far more often true that in a hetro marriage the wife will be the one who gives up their career path to take care of a child. Thus the court systems has standardized on an expectation that the mother will need spousal support, and child support in a divorce, because she is the one who'll need to retool and rejoin the workforce, while still _doing_ the parenting she did while in the marriage.
None of this happens in a vacuum.