Re: "even if there was no technical reason why it would."
And although a single international call will only be negligibly more than a local call, if 20% of the calls you are terminating originate from other countries that is a 20% increase in bandwidth required to service them, along with billing mechanisms, negotiation teams, accounts staff etc.
True, but there's a swings&roundabouts situation where outgoing international calls usually balance incoming ones. that's why, in the past, phone companies didn't cross charge. A call from, say, UK to France was charged at an international rate, and BT kept all the money. In the reverse direction the same thing happened, but France Telecom kept the money. It was assumed to balance, and apart from the Greek sexline case in Australia years ago that usually worked. Digital networks changed all that.
In general the main cost of a call, manual or automatic, is setup and billing. Once the call exists the per-minute cost isn't much different no matter what the distance is, but we still pay per unit time.