Even if they were aware that they are a US citizen, it is highly unlikely that they are aware of the tax consequences unless somebody explicitly told them. In

Even if they were aware that they are a US citizen, it is highly unlikely that they are aware of the tax consequences unless somebody explicitly told them. In almost all countries in the world, there is no good reason to renounce your accidental citizenship of a foreign country and there is no point in going through the trouble of doing so. And that doesn't even take into account the high cost of doing it.