You are right about this. Korea had several chances to score more goals, but they didn't know how to take advantage of the opportunities, unlike Brazil.
But I believe this is one of the main characteristics of an excellent football team, rather than a country that has a weak team, like South Korea (please don't get me wrong, I'm not belittling the South Korean team, i just made a brief comparison)
Their attacking lines are much different from Brazil, however, they may be under pressure to face a big team like Brazil. As we know that South Korea is not a big team with many excellent players. We can see only few of them that have good performance in the team. We can say that experience tells many things and Brazil has the big epxeriences. So, I think that the vitorcy of Brazil from South Korea is predictable enough even wiht many goals created by Brazil. But, we really appreciate how South Korea has qualified for round 16 so far, they were much developing.
We are very likely to watch an amazing semi final game like Argentina - Brazil.
This would be like an early finale in the World Cup.
I can't deny that Brazil is very awesome so far. They always perform very excellently, except in the previous match n which they didn't put their main squad. But, we know that many talents there, have strong attacking lines that always can utilize eveyr chance to score. In the next match, Brazil will face Croatia which they were the finalist in the FWC 2018. So, this will be interesting, right? Still cannot see who will be in the finalist because right now, we are seeing many big teams in the round 16, I personally expect that Portugal will be one of them, but I know, this is not easy