I think your OP overlooks how insidious this kind of thing is, particularly when you have kids. You start off in an equal relationship, then the woman gives up/takes a break from work during maternity leave and starts to focus more on taking care of kids as well as taking on a bit more responsibility for housework because they are at home all day/the mess is largely kid-induced/they feel as though they should because they are no longer earning as much/a combination of reasons along those lines.
The (usually) male partner gets used to having someone at home to deal with the kids/household admin/appointments/sticking a load of laundry on mid-morning, and if/when the time comes for everyone to adjust to the mother returning to work, there is suddenly a huge shirt required to get the relationship back on an equal footing.
In almost all cases one parent, and usually the mother, is the 'primary carer' and therefore ends up with ultimate responsibility for the children, which in turn means that they take on the shopping as a permanent chore because they are more likely to know what food fad is currently dominating lunch-box requests and who needs a quick dinner after swimming. They also find themselves doing the laundry because they know when PE kit will be needed or when a particular t-shirt will be requested for an activity.
In this way, any equal distribution of household tasks is suddenly dominated by the needs of the children (who cannot be expected to be responsible for themselves) and the 'secondary' parent sort of follows on their coat-tails, leaving the first parent surprised to realise that nothing happens unless they do it because they are effectively managing the majority of the household and their partner is able to get away with doing the bare minimum.
Coming back from that is a difficult business as it means that there has to be a mental shift as well as a shift in the physical business of actually getting the jobs done. I don't think many people embark on a completely unequal marriage and then wake up one day and decide that they aren't happy - I suspect that most drift into it without realising and only notice once the patterns are so ingrained that it is hard to change them without a major overhaul of the family dynamic as well.