The learning materials are all online, but realistically, very few students are going to work full-time 9 months per year for 4 years doing assignments by thems

The learning materials are all online, but realistically, very few students are going to work full-time 9 months per year for 4 years doing assignments by themselves, without weekly deadlines and friends to cheer them on. If you're going to put in all that time, you might as well get the degree. And as the article points out, the time itself is what dominates the total cost--not tuition.