They could promote policies to increase child birth among the native population and to foster a culture, including religious values, that support that. The justification that they need to import foreigners to support the elderly is nonsensical on it's face. If wealth is the cause of low child birth, what's going to happen when these immigrants achieve the same level of wealth as the native population in the next generation? The logical conclusion is that they are not importing these people to address the economic issue, but for ulterior motives, like diluting the native stock to diminish an ancestral identity that buttresses nationalism.