There is a practical fact that many of the US sellers do not deliver items outside United States, German sellers do not deliver outside Germany. While there is a potential interest from buyers from other countries.
Some sellers think that the internal market is enough, no extra problems with postage calculations etc. less to work! O.k., let the lazy bear to sleep, while some others are just afraid of international fraud, postal loss, investigations etc. etc. At the same time sellers from small countries like Latvia, Serbia, Paraguay, Laos, etc. mostly deal with foreign customers and many of them still do have perfect feedback! So it is not so bad and dangerous to deliver overseas !
Well, but speaking of international delivery, if the sales item is an expensive one, international buyers will (and must!) be ready to pay a kind of a secure delivery alike courier or registered mail. Then, why worry? Make the postage calculations and do deliver!
Good luck with internal and international sales!