You did not experience a trait of humans generally, but a trait of the specific, historically rare instance of high-trust society that had been consciously invented, built and protected, and that you were very lucky to be born into or live in.
Most self-forming human societies are high-trust and more loyal to each other than to truth (as the models have so eloquently regurgitated). Look anywhere from the hunter-gatherer tribes to villages to small towns. I have traveled my small, poor country extensively and the only place the fundamental idea of altruism had to be "consciously invented, built and protected" was in the big cities. In the rest of the places, it came to them as naturally as hunger. We've found skeletons from thousands of years ago that indicate that the whole society came together to care for the disabled individual for nothing in return, leading them to live as long as a modern disabled person with healthcare might.
Societies become low trust driven by specific factors: resource scarcity, something forcing a lot of different groups of people into the same area without integration. This is not a defense of humanity. I'd say the case of the returned wallet is more an example of class-loyalty than general human altruism. Humans have an instinct for exclusion of the non-conforming.
But the idea that civilization has to be invented and maintained is a debunked, regressive, even dangerous idea in that this line of thinking was used to justify a lot of atrocities historically.
Altruism, as you pointed out, is conditional. If population grows, the new constraints change the conditions that determine societal behaviors.
We need to develop tools to maintain a social contract once we grow past a degree of complexity.
We may be recreating the things we value from the small group stage, however our ability to achieve that in the recent past was an achievement.
It took a lot to get there, and tons of ideas and counter arguments were attempted and their failures learnt from.
Even the past moment had huge flaws.
I want experienced small acts of kindness in many countries and in both rural and metropolitan areas. I do agree that different societies are more or less likely. In my mother's travels, she was met with a lot of distrust in Guatemala (but this was reasonably recent after the end of the dictatorship), similarly my best experiences have been in NZ (just walking around with a map in central Auckland often ended up with someone offering to drive you to where you needed to go).
https://www.youtube.com/shorts/qG4RUBPypF4
I live in a high trust neighborhood. Bicycles will sit around for a week or two before someone finally returns. Outside my neighborhood bicycles last about an hour at most.
How is 24% a majority in your imagination?
In the micro level, Russians look to be lovely trusting people to each other. My source is an Instagram story of a guy pretending not to speak Russian, talking to drunk Russians on the street in English, and they're not agressive but they try to solve his problem. Yeah, great source, but I doubt it's much worse than yours.
A am not sure that is true.
I think we're living in a highly individualistic society and what little high trust remains is outside of the logic of markets.
You should have seen the dark age... if everyone fended for themselves there we wouldn't be here now. You know how much you depend on your peers without any of the affordabilities of today's age?!
Edit: it’s never “we’re becoming a low trust society because of rising inequality and K-shaped economic recovery leading to a breakdown of the social contract”, it’s always “we’re becoming a low trust society because of brown people”.