Why is it so expensive to send a letter from Chiang Mai to the USA compared to sending from the USA to Thailand?

The user is inquiring about the high cost of sending a letter from Chiang Mai, Thailand to the USA (1,500 THB), while contrasting it with the much lower cost of sending mail from the USA to Thailand (only a couple of dollars). The comments suggest that the user might be comparing different services (like DHL and the Thai post office) which have differing price structures. Users recommend using the regular Thai postal service to avoid high costs and mention that sending regular mail to the USA is generally inexpensive.