I had my child young. He is now a young adult and I am still of an age I could potentially have another baby. However, after 21 years of being a parent, juggling jobs etc, I am now in a position to earn more money, have nice holidays etc.
So in my eyes, I've done all of the hard part, why would I want to continue that responsibility if my child was to have a baby? Even if I was older, and retired, I'd see it as my time to enjoy life on a different level without that responsibility.
I never expected my parents to take on any childcare for the same reasons. That was their time after raising me all those years.
We all have a great relationship, so it has nothing to do with that.
If my child had a baby, I'd love it and have the odd overnight on my terms, and help out in emergencies. But that's all.
Think of how tiring it is for you now? Do you honestly believe you'd want to continue childcare for your own future grandchildren? It's even harder as you age. Also, so easy to say you would now, but you have no idea how you will feel in terms of energy when you are older.