Speaking English at home

Koreans are all about education.  Everything I read talks about how Koreans spend the most per capita on education, and in my experience here, it feels true.  Huge numbers of high school kids attend University, even the ones who are not academically inclined and would perhaps be better off just getting a job or attending a technical college to equip them with a practical career.  Children as young as 3 years old attend English and Music hagwons.  Older children do the circuit from English hagwon, to math hagwon, to science hagwon to music hagwon and finish it off with a dose of Chinese.  This is a daily affair, and ON TOP OF the regular day of school at the local elementary or middle school. 

I get approached by Koreans every couple of months, wondering if I will teach private English lessons to their kids ( I don't do it because it's illegal and I get enough legal OT at my uni to keep me busy).  The thing is, these people that approach me are fluent enough to have this entire conversation with me, in English.  In many cases, they work as translators or English Teachers, or are in some field like International Business. 

And so my answer to them is always the same: just speak English to your kids.  They'll pick it up, even if they answer you only in Korean.   Read English books to them when they're young, instead of Korean ones. Watch English TV or cartoons and cover up the Korean subtitles with paper.   The bonus is that these kids won't need to sit through some English lesson with me, or go to a hagwon. Plus, it's free!  And they'll be far better at English than their peers who attend hagwon or private English classes. 

For most of these people that approach me, speaking English isn't that difficult for them because they've mastered the basics and could speak it in their sleep.  Many of them have lived overseas.  I wonder why they don't speak it at home?  Is it laziness?  A non English-speaking spouse?  Lack of knowledge about language aquisition?  They are obviously not apathetic if they are willing to shell out  money so their kids learn English.  Bizarre. 

Anyone with insight into this phenomenon?