Generally, it is because of a multitude of reasons. Most Japanese high schools are private. Meaning that they have less restrictions on their curriculum and what happens in school than their public counterparts. read more
Most of the Japanese schools are private, after all, and thus, they chose not to have it. A few schools, I've heard, were seen to also have school on Saturday. Though most of these schools use that as normal school — not as detention. read more
I used to get them all the time in high school and middle school for being late to my first class in the morning, but I never had to write an essay for getting a detention. read more
Japanese students do get a five-week summer vacation (about half as long as America’s), but calling it a “break” might be a stretch— unlike in America, the Japanese summer break is right in the middle of the school year, and though school is technically out, students and teachers will still typically come to school almost daily for club activities. read more