Udemy and others, provides you with a long menu of topics to be learned with complete curriculums. You take your pick and learn what you want.
In comparison, College and University curriculums are not as deep and complete. True, you may take some other required classes and elective classes, which add up to the bill, but are these really necessary?
For example, Rob Percival's iOS 9 course is much more complete than Stanford's CS193P, the course offered through iTunes for free.
The question is: what is more valuable in real life: Acquired experience or a diploma?