why only US 
You've failed the Turing test.
Why the hell is it always US only 
?! The rest of the world exist too, and the US population is really small compared to it.
?! The rest of the world exist too, and the US population is really small compared to it.Because of this little thing called Customs, that makes you sign declarations under penalty of perjury so you open yourself up to prosecution for an effectively infinite/unknowable number of victimless "crimes".
Customs
Shipping within US - get accurate price quote online, get paid, print shipping label at home, drop off at post office 24/7, provide tracking number to other person
Shipping outside US - get not so accurate price quote online, get paid, go to post office during business hours, wait in line, determine which customs form is needed, fill it out, wait in line again, find out you didnt charge enough for shipping, go home, get emails other person asking where item is, provide them proof of shipping, get called a scammer
Additionally - I dont know what is legal to ship to your country and what isnt.
