Then the problem with case of yukkuri where they think "I have to eat" instead of "I need to eat"
Is there any animal like that too ? They're hardwired to eat all food available for them despite needing it or not. Normally there are limited food in nature so they will stop when the food is done and they probably won't find any food for a while. But when becoming pet they risk getting overfeeded.
Current medical research shows that women produce a hormone called oxytocin when breastfeeding. It's also known as the "trust hormone" because it apparently causes relaxation and feelings of affection while they nurse and may have an evolutional benefit of bonding. It's not hard to imagine yukkuri mothers feeling "easy" while the little ones are sucking her to death.