It is easy to procrastinate work.
Finding the motivation for something that is not due for weeks is very hard.
"Undergraduates represent 82.4% of the total population taking at least one course online"
This shows that the total population of students taking courses might be required to take an online course. This also shows that their whole education is not just online, it includes things that are learning in classrooms. If you take a student completely out of a classroom you affect the way they learn. This potentially takes the benefit out of courses all together.
In a classroom one can find social interactions with peers and adults.
If they sit at home they only have themselves to communicate with in person which is not healthy for a young mind.