I agree with M0nica and Madgran77 .
I think it has more to do with age than the mother/child grandmother/grandchild relationship. I would imagine if you compared the results of mothers’ of 4 year olds, to the mothers’ of 34 year olds, the results would be the same.
There was a time when I thought my son was the most magical creature to grace the planet. I was in awe of him. Now he’s 37, and whilst I obviously still adore him, I don’t have that same rush of emotion as I used to. I suspect my relationship with my grandson will evolve the same way, assuming I’m fortunate enough to see him grow into a man. I can’t imagine watching at him as a 20 years old, helping his dad dig the garden, and thinking he is the most adorable thing I’ve ever seen, for example.