When put into a regular high school there are not as many liberties as there would be if for instance the school were self directed and had some input into the child's education. Coming from a regular public school myself i can see the restraints and lack of interaction between student and teacher. Everything is standardized and made to organize students as cattle nothing is made to benefit and individual student, and intelligence is measured by one specific level.
Being in a self directed program forces a student into more responsibility than they can comprehend at such a young age. This places them in a situation where it adds more stress to the student at a higher rate. Without the maturity to factor into this type of program creates a pedestal in which the student is bound to either not do well or suffer anxiety, stress, etc due to the expectations required from them.
We need the regular schools in order to help students who may be struggling and a self directing high school would not cater to the needs of every child as they all have different learning styles.
Another reason it shouldn't exist as that teachers would lose jobs therefore increasing the unemployment rate.
Some function well in a self directed situation. Others become totally lost and need a greater deal of structure. Most teens are not able to choose what is best for them yet as this is a later life skill to develop. If these schools exist they should exist alongside normal schools.