I don't think people are all that much kinder and care more about their community overall, but rather big cities puts people into "survival mode" a lot, where we are trying to cope with too many people around.

It'd be exhausting to acknowledge everyone we pass, much less great them in a friendly way. It'd be exhausting if everyone asked you if you need help (and so too few end up doing it instead) just because it's obvious you're having a bad day.

And sheer numbers means running into the occasional people trying to scam you etc. is much more likely, and another reason for people to be more sceptical of your motivations etc.

Get past the shields people put up to cope with this, and there's plenty of kindness to find in big cities too.