This is so she can avoid having to once and for all have the characters confront bad habits that they got into. First off, John would finally have to face up to the fact that he'd blundered into a self-made omnishambles by his unprofessional habit of complaining about his wife and children because he's all butthurt owing to their not being the media stereotypes he needs them to be to feel that his life is going the way it was meant to. Elly is supposed to be happier than she is and the kids are supposed to find manual labour sheerest mindless bliss and since they're the people they are instead of the sitcom morons television told him to expect, he gripes how irrational they are. His non-stop grumbling about having a life most people would envy makes it damned easy to believe that yes, he would run away from home with a floozy when asked to change a diaper.
Of course, that would mean having a work wife whose role appears to be delivering withering sitcom put-downs about how ungrateful he is except when it mattered. When he's merely beefing about how oddly unhappy Elly seems to be all the time, she's quick with a quip but when he started saying something that hinted that he was doing a damned sight more than complaining, she became as strangely passive and furtive as the woman he's actually married to. The whole blasted thing would have been prevented if she'd done more than huff "MEN!!!" when he talked about how great the apartment was. That can't happen because of a weird and stupid belief Lynn has: one must never directly confront anyone you are pissed off at or else some undefined horror will be visited upon you.