You are a little confused as to the purpose and function of the global shipping program.

A large percentage of U.S. eBay sellers don't ship outside the U.S. Its no different in Canada where most eBay sellers also do not ship internationally. This is do to the extra work involved in doing international shipments.

The global shipping program allows sellers (in most countries) to ship internationally without having to do the work themselves.

The actual shipping cost and import charges are only slightly higher than you would pay if the seller didn't use the global shipping program and did the customs work themselves.

For the most part it is always less expensive to purchase from a seller within your own country if the alternative is going through the global shipping program. But there are times when you can't find the item in your own country.