I wonder how humans survived for the first, oh, 99% or so of the time we've been on earth?

Prior to the automobile era, we were all pedestrians. A small town was a town you could walk the length of. Europe is dotted with old villages denser than contemporary North American cities.

While true, I suspect most of the people who are looking for walkability want something more than a small town with a pub, a small market, and maybe a couple other stores/cafes/etc. I've stayed in many of those small towns and they can be very pleasant--but there's not a whole lot within easy walking distance.

My partner and I were looking for a walkable urban neighborhood but ultimately ended up in a small town with a pub, market, cafe, store... and a train to the big city.

Couldn't be happier, but I wouldn't recommend it to someone who is single.

Likewise, chose a cute little New England town when I realized that the benefits of living in a city are mostly... drunks, drugs, and concerts that are neat, but I'm unlikely to attend.

There's culture and museums and lots of different food in cities, but all I really need is a small smattering of decent establishments in exactly the vein you just mentioned. And of course a good environment for working from home.

Same. Given our requirements and price range we would not be living within walking distance of the city museums or cultural amenities anyway, and we would be about as far a walk from the closest supermarket or cafe as we are now.

I think there is something to be said for New England towns where the design of the town center predates the automobile and is therefore pleasantly dense and walkable. They just don't seem to make towns like that any more.

If you can be 100% remote and don't need the transit options to the big city then just a little further out you can find charming towns for even less.

Depending upon circumstances, there's certainly something to be said for spending money/effort to go into a city now and then rather than spending an ongoing premium for living there day to day which may even have certain negatives.

We've been driving to costco since neanderthals walked the earth

For sure, not by living in car-centric cities.

We survived in little pedestrian-only villages. That thing that now is considered luxury or even a tourist destination.

Barely. The humans certainly would not survive in the current numbers/concentrations, without all the civilization around them.

For all that time, people had to walk to wherever they needed to get to, so yes, they had to pick places where what they needed was close by.