Not everyone handles sleep deprivation the same. Not every baby sleeps the same amount or at regular intervals. Some babies just never seem to sleep or have weird needs that require exhausting accommodations. It’s terrible, but new babies are so vulnerable and there are so many chances for failure at the same time parents are at their most compromised. I have sympathy for the stupid, addled, forgetful mistakes anyone could make under constant, chronic exhaustion.
We were never meant to do it alone, the nuclear family is a myth.