Babies are incredibly difficult even in the best case. Sleep deprivation is intense. Breastfeeding is difficult. Adding in small additional difficulties adds up. "This is a bit more difficult" becomes a huge mess when you are on three hours of sleep and there are 10 different "this is a bit more difficult" things that people are suggesting to you.

Add this on top of any sort of complex baby (illness, allergies, colic, slow weight gain, etc) and suddenly the slightly less complex disposable diaper becomes a godsend just to save a few minutes or a bit of mental load.