It seems to me that when you interact with fewer people per day, you can put more time and energy into courtesy. There's also a higher chance you'll run into so

It seems to me that when you interact with fewer people per day, you can put more time and energy into courtesy. There's also a higher chance you'll run into someone again, so there's more incentive to treat strangers well. And small towns tend to be less diverse, meaning there are fewer incidents of rudeness resulting from different cultural expectations.