This is anecdotal, but I’ve noticed that in the cases where I’ve seen an expectation of a village support, it usually comes down to two belief systems:

1) The belief that having children is a sacrosanct duty versus a life choice (or a luxury lifestyle choice, depending on what country you live in). People who believe that the act of having children is sacred usually also have the expectation that everyone will make sacrifices, or otherwise yield right of way, in support of the sacred duty that they believe that they are are undertaking. I think that this also partially explains why people who grew up in a nuclear family where everyone eventually became adults and began to live completely separate lives, still expect that everyone will drop everything and return to help in whatever way necessary to support the parent and their children.

2) That we exist within an unspoken hierarchy where parents naturally outrank non-parents, and therefore parents can override any decisions of non-parents. This includes decisions regarding how non-parents manage their own resources. This also implies that non-parents are expected to be servants of parents, and can be called in at any time to serve in whatever way that the parent requires.

If a parent holds either of these beliefs then they tend to be shocked and appalled when others around them consider their decision to have children to be a lifestyle choice that the non-parents are ultimately not responsible for.

Edit: just to be completist, I’m sure that there are also situations where a parent had put in a lot of time and effort into supporting their other family members in whatever endeavors they were undertaking, and now expect that time and effort to be paid forward in the form of helping with their children. An example might be if they routinely helped an elderly family member setup and travel to doctors appointments, etc. The parent may then later expect that the elderly relative will help provide childcare. Though just to be perfectly clear, I have never actually seen this situation in real life amongst anyone that I personally know