That's cos no matter she's a Kardashian, she actually has maternal instincts. And I'm no fan or her at all but she's more of a Mother than Kim will ever be.
I love how Kourtney goes to places and carries one child, holds another's hand and keeps the third relatively close. Everyone is interacting.
Those pics of Kim/Kanye getting out of the car, Kim is on the sidewalk while North is in the street, still closing the car door? Then Kim is in the street while North is on the sidewalk. Kim never looks like she's having fun with the family.