[0] A mile is essentially the farthest the average person will comfortable walk versus driving a car for travel that does not require carrying anything back. Once you add in carrying things (e.g. groceries) it drops to half a mile. Anything less dense than that and people won't want to walk, anything more dense than that and you're into standard city planning.
[1] Assuming you're American of course and obviously I'm not about to ask you to dox yourself, considering this type of thing can vary right down to the neighbourhood level.
https://en.wikipedia.org/wiki/Murder_of_Kitty_Genovese
If you pack people in too tight they just tune each other out.
If you can walk to these things, you don't live in the areas the parent comment is talking about. "Suburban sprawl" doesn't mean all suburbs, it's specifically the ones which don't have facilities and community.
It might be a composite effect of different things contributing to the easiness of being alone. Cultural skill that overtime gets eroded, and as less time people spend among others, it becomes even harder to go back.
We need to do things ourselves.
There are lots of libraries with cafes, maker spaces, and more. Seattle is one.
If yours doesn't, this is your wake-up call to get involved with your local library. Stop waiting for someone else to do things.
There is no maker space listed at https://www.spl.org/programs-and-services/a-z-programs-and-s....
Within KCLS, there are two public libraries that have maker spaces (AFAIK): Bellevue, Federal Way.
PS this is not meant to be confrontational, would love it if there were more maker spaces in libraries (when have asked in the past, the usual answer is that they do not have enough space for it).
Don't think you have to live in some idealized fantasy land to go talk to your neighbors.
The city added sidewalks there in the '00s or so, but when I go back there I almost never see anyone using them.
I think the trend of isolation and loneliness is not really related to infrastructure or stuff like "walkability." Those things are pretty minor obstacles.
I lived in a car dependent burb for 20+ years and would rarely, if ever, run into my neighbors out on the town. Living in a walkable neighborhood in a medium-low density city for under a year and I regularly run into my neighbors.
Never seen "cul de sac" in English before...
For what it's worth, many (most?) countries have most of their people living in places that are not sprawling suburbs. It's worst in the "Anglosphere" countries (US/Canada/Australia) within the last 50-70 years, but it's absolutely not a fantasy land. It's the way things were everywhere before 1940, and most places still are today.
I say that because it is fixable, if we let ourselves fix it...
Your point stands though, even in a fairly antisocial layout of a suburb, you can still usually make friends with a decent number of people nearby.