I think this is partially the one-child syndrome. My wife’s best friend and her husband have only one child. They’re nice people, but the mom has literally never “missed bedtime” with her kid. They’re afraid to break the routine. When I told my wife to invite her friend on a girls weekend trip, my wife said she knew her friend wouldn’t go because of this. Shackles of her own making.
All the most overwhelmed parents I know only have one child each and I don't think this is a coincidence.