Because people have cell plans (and no land lines anymore, like most places) that they brought from their own country or region that a lot of the time a phone call would be long distance. Or have text fees for reminders, or a combination of both. So the solution, a long time ago, was a single method that has no fees for either.

sure but first, as an american, you have to make sure the doctor in question is ‘in network’

Imagine if every state had a different cell phone carrier or go back even further to when it was long distance even just blocks or cities over. Now imagine a technology comes in that doesn't care what carrier you are on, or if it's long distance.

That is kind of what happened to countries. Especially if you have people who work in one and live in another or have clients in another.

So even though now maybe it isn't long distance, or carriers talk to each other, everyone is used to the way they have been doing it for free.