In South Korea, 69 percent of adult smartphone users use a Samsung device, while only 23 percent use iPhones, a Gallup survey of 1,001 adults found. But the survey reveals a starkly different trend in one demographic: younger millennials and Gen Z. Among the younger generation, aged 18 to 29, iPhone...
A bit weird to see LG in the charts (given that they're out of the smartphone industry now) and yet none of the other big manufacturers (Xiaomi, Huawei, Google).
The brands you mentioned aren't widely available in Korea. Since LG left the market, all the carriers, to my knowledge, only offer Apple or Samsung devices.
You can buy unlocked phones of other brands like Google or Xiaomi on the Korean equivalent of Amazon (Coupang), but they're substantially more expensive. I'd bet you can get Chinese brands at the little mom and pop shops that cater to Chinese students and immigrants.
I believe LG is also a South Korean company compared to the Chinese ones you mentioned so maybe there is a little patriotic incentive for LG over there.