You know, alot of people point to many things NA/EU lack that makes Korea so much stronger but people are ignoring one of the simpler points that makes Korea a dominant region.
In Korea, you cannot have a bad week. You lose two games and your on the verge of dropping out if not gone. In NA/EU, you can be second entire split and it won't matter, or if you have 7 game losing streak. NA/EU just isn't built for to breed talent and competitiveness like Korea is.
I think people overrate how much coaches at the elite teams are prepared to kick players for one off split or series. Consider Najin Shield, where the coaches have stuck with a seemingly mediocre team for a long time and they've developed into an elite outfit, or players like Space who've stuck around despite not setting the world on fire. SKT K haven't changed their roster since formation, give or take ManDu's time off, and the Samsung teams opted to swap their mid laners across rather than release one of them. Obviously first team players do get released for not having the necessary mechanical skill, but this has been happening increasingly frequently in NA and EU without the overall level of play noticeably rising, given Fnatic and C9, the dominant teams, haven't made roster changes for a long time (Rekkles was always coming back for Puszu once he was of age, so the only change since the start of S3 for Fnatic was Yellowstar -> nRated).
What does get punished severely though, are poor attitudes towards your teammates or towards practice (I don't think you'd get away with turning up hungover to scrims, as Fnatic players reportedly did recently...), which is what
SaintV and
Hotshot have recently claimed often go unpunished when players are in charge. League seems to be a game where good attitudes, planning and teamwork are more important when it comes to improving than gathering the absolute best individuals (e.g. SK Gaming coming 2nd this split in EU with a group of largely unheralded players). The population density, culture, and high playerbase definitely does mean the scene is brimming with talent and competition, in a while NA and EU are not and likely can never - I wouldn't deny that at all.
Another big difference is that the Korean e-sports teams pick up promising players and train them as subs for several months before releasing them into the team, instead of relying on them to come fully formed from amateur teams.