From an interview with the author: https://www.weforum.org/stories/2022/09/young-global-leaders...
[1]: https://taejun.substack.com/p/founders-peak-speech-script
I do find it quite unusual that he would not be allowed to naturalize after living all his life here and being married to a Japanese citizen, so perhaps there are other exceptional circumstances. Or perhaps his statelessness isn't something he is actively trying to resolve, having found ways to work around it when he needs to travel and do other things.
Unrestricted jus soli (extending nationality unconditionally to those born in the territory of the state, regardless of ancestry) is largely an American (as in "of the Americas", not merely "of the United States of America", though the latter is a significant reason why it is true of the former) thing, though there are a few countries outside of the Americas who do it as well.
Some more countries have restricted jus soli, extended to those born in the territory of the state only if the government judges them to be ineligible for nationality by the law of any other state, or perhaps only if the parents are actually stateless, as a way to mitigate statelessness. (And states who have adopted a rule of this type for this purpose may have done so after the UN Convention on stateless persons in 1954, and may not have applied it retroactively.)
Practically, there is no point for the state to deny you citizenship if you went to school there and can do some kind of a job and pay taxes, because they can't even deport you to a country of origin if you are stateless and born there.
Technically even the US has the jurisdiction qualifier, which the orange clown wants to abuse.
I know someone who tried to start the naturalization process but was instantly shot down for his Japanese skill (he speaks Japanese well). I know others who have lived in Japan for decades but cannot apply for permanent residency because they only receive short visas, making them ineligible.
Immigration officers have ultimate discretion and will not explain themselves to applicants. I assume this is by design so that particular 'standards' can be subtly applied without being reflected in statistics or receiving any criticism.