High School phase is a stage in student's life where he or she has a life goal and his own routine to achieve that.If on a certain day,he feels that the school classes are not important for him that say, he must have the eligibility to be absent.Compulsory attendance in this phase is like messing up with the student's self-planned routine for his goal and decreasing it's effectiveness by imposing our own routine on them in the name of expert guidance.
Forcing student to learn when made to go somewhere against their will may seem like pushing the student to their potential, but it can actually backfire where the student now resents this and will probably try to forget what was learned.
Not a super good example, but growing up I remember having to do book report after book report, and reading was hard for me. The writing came easy, the reading was difficult: reading the same lines 3-4 times, not always understanding the materia, dyslexia. In high school got the help needed, but that reading experience made have a huge disdain for reading for a long time. It wasnt until my mid 20s about ten years ago that I started to like to read again - though its hard for many books to keep my interest past the first two chapters.
I will say one English teach in particular at my high school was my style of teacher: Class Book Reports. It wasnt homework, but a portion of the class curriculum and the way he divided up the book and class and taught the material helped me emmensly.
If students didn't come to school, teachers who teach more physical things would lose their jobs as they would be teaching no one since students aren't there. Sure the teachers can send the students emails of what to do, but the students wouldn't learn anything without a proper demo, therefore, teachers wouldn't teach anyone ending in the teachers losing their jobs.