A lot of SK's foreigner workforce are unskilled laborers from poorer countries. So one explanation could be work related but unspecified due to company reputation or that no one simply cares about poor foreign workers.
I believe South Korea (like most industrialized countries) does not offer single-payer health insurance to most foreigners, who either have to purchase it themselves or go without. It seems likely that a large number of foreign residents get sick and never go to a doctor. Without a medical history it's not easy to determine a cause of natural death in an older sick person, even with a good autopsy.
I wrote "taxpaying foreigner" as opposed to "permanent resident" because most industrialized countries do indeed offer their healthcare to non-permanent residents on work visas. For example in Ontario after 90 days you have access to single payer healthcare. In France you get it after 3 months, in Spain after 2-6 months depending on the locality, etc...
Don't always need to be permanent. 2 year work visas will often get you covered, caveated with the idea that you're working a job and paying taxes.
many educational visas also cover this, depending on where you're going and where you're from. e.g. Most Europeans in Australia on valid visas have coverage due to reciprocal agreements
https://www.chosun.com/english/industry-en/2024/06/26/IL43VM...
https://www.latimes.com/world-nation/story/2023-10-30/south-...