There is a possible flaw in the statistics. In many cases it is simply ...the customer walking away. (not the student failing)

For example not everyone is after "credits". I have enrolled for some online courses and have found the quality of instruction low, or the pace wrong for me. As my purpose was to increase my knowledge, I just bought a couple of books on the topic (much quicker and more in depth). On a current course with coursera, I am enjoying the course and the lecturer Michael S. Roth, especially as the course is diametrically opposite to my day to day working life. Not too sure if I can afford the time to write the essays for the assignments.