Courtesy and friendliness are two-way streets.
My daughters had the same experience. People were wonderful to them.
I suspect that those who treat their hosts with respect and admire the country they visit, rather than expecting things to be like home and expressing disappointment when they aren't, are more likely to elicit the better nature of their hosts.
There are jerks everywhere, and I imagine perfectly lovely people will run into the occasional jerk when traveling. When someone runs into nothing but jerks, though, I wonder whether they are drawing out the inner jerk among those around them by their own behavior.