Because the nationalized airlines in other countries are doing, what?
One reason why nationalized airlines "work" (using that term loosely because they really don't work that well) in other countries is because many of those countries have a single major airport that serves the entire country. In addition, many of those countries have (or had until recent years) a single airline.
The U.S. is completely different with hundreds of airports and dozens of airlines. It's a completely different market where "top-down" centralized control just wouldn't work.
This is why nationalization works in some countries (Poland, Thailand, The UAE, Indonesia, Malaysia, New Zealand, and Singapore among others) and not in others.
That's debatable. Israel has more than one airport. China (obviously) has many airports.
As a broad generalization it does work in some cases.
But like many things, it doesn't work in all cases nor circumstances.
In regards to the airports, I believe he may have been referring to major international airports, i.e. Thailand has BKK, Poland has WAW, Singapore has SIN, Finland has HEL, and Malaysia has KUL. As such, the aforementioned airports handle most, if not all, of the major international traffic coming into and going out of the selected country. And while there are other major/large airports, they often don't handle nearly as much traffic as the main international airport.
China is a special exception; but then again, when isn't China a special exception? LOL.