ill tell you why Korea doesn't really have any good athletes (besides woo sanghyeok)
the korean way of developing athletes is just toxic. athletes with any kind of potential start training seriously from elementary school, and almost train like pros (even at that kind of age). they are moved out from normal schools, and get to attend specialized sports schools where you learn the bare minimum. coaches have them do insane workouts, and give them an insane workload. in many cases, coaches physically (and sometimes, sexually) abuse, not to mention the psychological pressure that could even put alberto salazar to shame.
by the time these athletes are out of high school, theyre done with this kind of life. their bodies and minds are cooked; years and years of hard training burns them out. the few that continue into adulthood are overworked, and quite honestly, do too much. 3 tough workouts in a week, with 2 of them back to back. theres not much recovering happening...
my colleges' records are better than most korean national records.
contrast that with what I do in college, its completely different. we have 2 days of working out, and the rest are just easy runs. its all very simple. workouts are tough, but leaves you fresh enough to get out the next day. all this, while balancing a full load of coursework (were d3, so no shortcuts)