> the digital nomad isn't participating in the local labour market.

Yes he is. If the firm's willing to employ someone in Costa Rica, there's no reason it couldn't be employing a local.

This is the typical communist/labour style answer which ignores that todays mobile work force is not just a body in a geography. An employee past about 5 years experience is essentially unique when observed across the many variables (education, years of experience with each specific tool, industry/domain experience, soft skills etc). Just because a capable expat employee happens to presently be located in Costa Rica, doesnt mean a capable Costa Rican can be found. The most valuable people in the workforce are not cogs.

Adding to this, those employees are, themselves, probably working for an American company instead of a local one.

There's no reason it couldn't be employing a local, but there are an awful lot of reasons it wouldn't. No locals applying chief among them. If the company was explicitly not hiring anyone from Costa Rica, sure, that would be one thing. If the best candidate happened to not be Costa Rican, that's something else entirely.