Attending your classes in high school is mandatory, because students are regulated to go to school for a certain amount of hours or days depending on your state and school district. The non flexibility in high school is mandatory because these students are still children, but that debate shifts once students reach a high education level like college. 

These are adults, not children, and making attendance mandatory creates more problems than it solves, and the whole point of college is becoming an adult and making hard choices on your own. If attendance at universities became mandatory students would be losing some of their freedom, as many students at universities are molded into multiple different participants of each club or student organization they are a part of. Along with students who have all different learning styles. This makes all students conform to a system that might not work for them. 

Along with this is the money part of college, if students are feeling like they are mandated to be in a classroom, they might not get anything from it and let their grades slip, causing the retake of the class. The last reason is that if attendance is mandatory the higher education is shown more as a hurdle to jump over, then a gracious opportunity. While mandatory attendance may seem like the best opinion for some universities, it’s not looking too great from a wider perspective.