1) You are a foreigner and have novelty appeal over a local, so they see you as a chance to practice their English and learn about your culture. Many also feel obligated to treat foreign visitors with hospitality too, so they try to be extra nice to foreigners so that they will have a good impression of their country. (e.g. white people in China and Taiwan usually get extra hospitality from locals)
2) They perceive some potential benefit from knowing you. If they are from a less developed country, they think you are rich and so your money gives you social value. Or they may be hoping to get a visa or green card to America or a more developed country, so they see you as a ticket to move abroad for a better life.