IMO the problem is with the meaning of "setting boundaries and expectations." Boundaries are basically, "If you do A, I will do B," or, "If you do A, I will not do B." If you keep leaving your dishes in the sink, I will not wash them, I will only wash my own dishes. That sort of thing. You can't just SAY "this is my boundary." You have to DO something to enforce it. But, once you bring children into the mix, it becomes exponentially more difficult for a mother to set boundaries because that impacts the children. "If you refuse to take a day off work to look after our kid when he/she is sick, then I will..." what? If your husband refuses to take days off to look after a sick kid, what exactly are you, the mother, going to do? Go to work anyway, leaving her sick child at home alone? No, obviously that is impossible. Indeed, unthinkable.
Once there are children. a mother's ability to set boundaries is constrained by the needs of her children. If you refuse to clean the house because your husband doesn't do his share, then your children will live in a filthy house. If you refuse to change the baby's diaper because your husband refuses to do his share of diaper changes, then your baby will eventually become ill from the hygiene problem and someone will call CPS, whether the daycare, a neighbor, the hospital to which you take your sick kid. Even if you divorce, as a way to attempt to set boundaries, you cannot force a man to parent. You'll STILL be left doing all the mental load, childcare, possibly (depending on the child, your access to support of your family, etc.) unable to earn enough at your job to support yourself, etc.
I think if you work through the implicit parts of this, you'll see that a huge part of the problem is that many men (not all men, etc. yada yada) just don't care enough about their own children to want them to thrive. They'll put themselves before their kids. Some women do this too. But, on average, more men than women, and fewer women than men.