I too have signed up to a mooc, simply to watch a particular lecture or two on a topic - as recommended by colleagues or friends. No intention of completing the course, and in fact very happy with the content.
Perhaps they need a box on the signup or viewing form, to indicate "just checking it out to see if I'm interested", or "just here to watch part of the course".
Here in Australia, when students finish high school and enter university it is common to hear them given the advice that it is "okay to change" after a year of your course. Get a feel for it, decide if it is actually for you, calibrate against the teaching/learning style, measure the enjoyment vs effort etc. I imagine MOOCs are starkly in contrast (provide an email address) to the complexity of signing up for a university degree.
Who knows, maybe students even form opinions by partially completing MOOCs in topics they might want to study at a tertiary institution!