Well, a support network is one thing. My grandparents certainly babysat me on occasion, but me and my partner are quite far away (over an hours drive) away from any close family. Naturally my parents are also a lot older than my grandparents were as well, so it would be less fair on them.
I really don't think the phenomenon of people having fewer kids or having kids later is a mystery!
When I was growing up in the 80s, working class neighborhood, most wives had a part time job. Whoever was off that day would watch the kids. I remember sitting in random houses with 7 or so other kids, eating mac n cheese or bologna sandwiches, waiting for our moms to come pick us up after work.
As an adult with my own kid now, it would seem such an idea is a pipe dream.
Yeah, the decline in neighbourlyness would be an even more interesting phenomenon to study.
My person hunch is back in the day there was a more "we're all in the same boat" feeling at the street level, where everyone had similar socioeconomic backgrounds whereas now that's not true at all.
In the past, in the UK, everyone living in a road may have had the same landlord (the local council) but now you can have multi-millionaire with a £50K car living next door to someone in an identical house who is renting privately, on housing benefit, taking the bus to their minimum wage job, and struggling to feed their kids.
People are much more willing to give and receive help from their "peers"
I don't think that's the only factor. I think it's also just culture.
I grew up on a street (in the US) where many of my neighbors did have the same landlord as my family, but none of us spoke to each other; they were basically strangers like any other.
I was born in 2003, so this is more recent than the 1980s.
I really don't think the phenomenon of people having fewer kids or having kids later is a mystery!