If you had a baby, you wouldn't want them woken up in the middle of their nap by someone coming home and turning on a TV, closing a door, or something else equally normal. If you had children, you'd want them to have a quiet place to study and rest, even when the twenty-something neighbors are throwing a raucous party.
I think most people, including parents, both don't want to be disturbed and don't want to disturb others.
Apparently if you go about your normal day, babies will get used to falling asleep in a semi-noisy environment. However, you go out of your way to create an ultra quiet place when they sleep, any slight disturbance will wake them up.
For me, this would be the goal. Being able to hear the next room over for loud noises could be a safety issue, but hearing my neighbor has never been a positive. I can see zones of sounds inside a dwelling (e.g. kitchen - dining room - living room sound separated from bedrooms or office).
Every single time I've done it, they've apologized, turned it down, and usually thanked me for doing it myself instead of calling the cops.
I've lived here for about three years now. It's a smaller pile of anecdata than yours but I don't feel like I'm likely to see a different trend any time soon.