She has a hard time growing a new social life because the kids are always there. Depression is two to four times more common in women than men, depending on whose figures you like, and she's got reasons to be depressed. No retirement, for example. She gets a prescription for lithium. You can't divorce a car payment.
Days only have twenty-four hours.
She doesn't have time to be a full-time mother and have an adult's social life. Often motherhood draws the short straw. She starts leaving young kids alone for long periods while she goes out. By no means all divorced mothers do this, but more do than the newspapers tell you. Latch-keyism becomes inevitable.