Too Broad means that the question is Too Broad to be answered with a single answer. In this case, someone could realistically answer differently for each country that does not allow renunciation of citizenship.
This is really two questions:
- Which countries don't allow renunciation of citizenship?
For any particular country, the second question is appropriately scoped. But the first question is a list question, which is often Too Broad in and of itself.
Note that even limited to a single country, the second question could have multiple answers, e.g.
- Historical reasons. Individual to each country.
- Legal quirks. Individual to each country.
- Possessiveness. Taxes, mine!
It also leaves the question open to theoretical answers. For example, someone could speculate that a country wants to recover the funds spent on education for its citizens.
A country could want to use that issue as part of a larger negotiation, again specific to a single country.
Some legal avenues may not have been tested. For example, in the United States, it is not necessarily possible for a citizen to renounce citizenship. Under the fourteenth amendment, everyone born in the US is a citizen. But the US currently allows people to act as if they renounced their citizenship. What happens if someone renounces their citizenship and then later reclaims it? There is a fourteenth amendment argument that they're still a citizen. There's no renunciation exception in the text. That's on-topic to the original question, even though it has no current real world application.
Note that the last has important ramifications for visa overstays. To get around the constitutional requirement for birthright citizenship, the US could have female visitors sign a preemptive renunciation for potential unborn children. And could have deportees agree to renunciation to keep their kids with them and out of the foster system. So the courts may be reluctant to go with the simple solution of allowing voluntary renunciation.
And that's about a country that at least nominally does allow renunciation. I could easily write a full length answer just on that basis.
Too Broad does not mean too difficult to answer. It means that it is too easy to answer. There are too many possible answers. Switching to a different kind of subject expert doesn't fix that. You need to make the question more focused, perhaps such that only that kind of subject expert could answer it.