Why different rates for non-domestic calls?

What is/are the reason(s) that most companies offering computer phone calls, including Fongo, limit no-extra-charge recipient numbers to *one country*, typically the country the company is headquartered in.
Is it a commercial (because they can , it reduces costs and increases profit to charge for other numbers), a legal, or technical reason? Or some combination? Is it purely business or something to do with gov't regulations and monopolies?
I read somewhere (maybe it is not true) that there is no technical reason anymore that a long-distance call should be any more costly than a call to your nextdoor neighbour.
Is it a commercial (because they can , it reduces costs and increases profit to charge for other numbers), a legal, or technical reason? Or some combination? Is it purely business or something to do with gov't regulations and monopolies?
I read somewhere (maybe it is not true) that there is no technical reason anymore that a long-distance call should be any more costly than a call to your nextdoor neighbour.