I really have no horse in this race, but would have found the discussion to be interesting if everyone weighing in started with their age and the time period their parents and grandparents did or did not help. I think that has a lot do with where the person is coming from.
I'm late 40s, DS is 10. We always had paid childcare for day to day stuff. SIL on his side babysat overnight once or twice a year to give us a night out, starting when DS was 2. (we had done likewise for her lot in the years before)
MIL did after school pick up one day a week - we didn't need it but it was engineered to get her back out of the house again after being widowed. And now she's passed away DS has such fond memories of hanging out at his nan's.
My own DM stated that she wouldn't babysit, and she's been true to her word. Not even in an emergency. Now, in her case, she was in the older group of kids in her own family so basically reared her younger siblings from about age 5 herself. She was forced to leave school to bring an income in to help support the household and the younger ones with money and hands on help. When she got married she quickly had loads of her own in succession. So I can fully understand she wants a child-free retirement and support that.
However, I won't lie- it hurts when she wouldn't help us in a genuine emergency, even once, but would happily hop in her car and drive for several hours to my sisters house to babysit because 'she needs a night out'. She's also babysat every single other grandchild several times a year. So the 'no babysitting' only really applies to me. But I also know that should DM require elderly care, she will point blank refuse a residential place, would not dream of imposing on my sister so it will fall to me likely to move her in with me, rearrange my life and home to cater for her needs. She's already starting to have an expectation that I can take my annual leave for her ad-hoc needs so expect that as she requires increasing care it will be a well established norm that I drop what I'm doing to do her bidding...