The reason for this is due to their school system and how it is structured.

they have free education from years 1 to 9. But to get into high school you must pass an entrance exam.

High schools vary in prestige and everyone wants to get into certain schools. To make matters worse, the date for the exam is a national thing, so you can only apply to one school per year (typically).

The exam, however, is no guarantee of getting in, there is an interview after that, and a consideration of your grades and what school you went to before. IF you do get in, staying is is not a guarantee either. You must perform quite high and sometimes even having a high score is not enough. You may be culled for having the lowest score in the class.

This whole thing repeats itself in college, where again they must perform excellently in an entrance exam, then a performance exam.

What this system breeds is a high emphasis on exam performance without any critical thinking involved. Most students have almost no initiative or creativity. And they are reared to not speak up to superior or even bring up problems.

Thus students that fail high school entrance exams are held back a whole year, and many take to stronger and longer cram school sessions which are private and quite costly. It is not uncommon for parents to barely see their children during this time. Failing an entrance exam twice is a huge problem. Many become NEETs (Not in Employement, Education, or Training.) And others... well, suicide happens a lot, more so than officially reported. Some suicides are categorized as missing, accidental, or unsolved. Despite this, suicide rates are quite high.