...in my opinion. To me, it seems clear that a good formal education is simply a vetting process. Specifically, a provision of a certification of work completed by an accredited, dispassionate entity. It has very little to do with teaching. Universities expect students to achieve passing grades in their classes regardless of how much or little the professors of those classes are interested in actively teaching versus simply requiring students to cover the material on their own. It also has very little to do with learning. Anyone can learn, say, architecture or mathematics independently of a university. While that is great it, in reality, means very little if there is no one can verify that you did in fact learn it, i.e. no one is going to have you design their building just because you say you know how. While employers or even universities (for advanced degrees) could attempt to verify this knowledge independently, it costs a lot of money and quality of that would be all over the board. However, universities really can't say that students learned the material, either. They can just say that students completed work that should require knowledge of that material. This is why cheating wrecks the system, i.e. it is a way to complete the work without the knowledge.
Universities exist for this verification process and are accredited based on the quality of this verification process. That is, they are not just trying to be greedy or hoard knowledge nor are they trying to provide great environments and contacts and experiences. Rather, when they issue a degree they are signing off on a person. If that person doesn't know what they said the person should, it diminishes the perceived quality of their degree.
The point: it is very difficult, and costly, to provide the same quality of verification with online classes as you can with face to face classes. Cheating becomes a much more prevalent factor. Getting more and more students through the courses increases the likelihood that a false positive will be issued. Evaluating a student's commitment to their education is more difficult when it is impossible to determine how much time the student has spent "in class", i.e. viewing lectures. And more. This is why universities hesitate to go that route.