We have done the school run for our 8 year old GD AND nursery runs. It is simply the case DD has always had to work to provide for the family and you all do the best you can.
I have to say my parents did exactly the same for my DD, 30 odd years ago. It most certainly is nothing knew but maybe those who could afford not to have to go to work, have over the years diminished some what in numbers.They are only having to live their lives as many have had to do for years.
You can't 'force' grandparents to give up work to look after their GC surely. You are either prepared to work together as a family unit and make choices or you, as some do, say no. I think in a lot of cases the GP's have retired early and are in a reasonable financial situation to cope. That may all change as the pension age increases and there will be fewer GP's at the school gate and a new circle of life evolves.