Why don't I see more people using The Great Courses?

[diminutive]

Its perplexing to me that I don't see more people taking advantage of the Great Courses series of lectures. They're super expensive but only if you purchase them straight. You can get them for the price of one Audible Credit or often for free at the local library. So far its helped me immensely on the Civil War and Soviet History DSSTs as well as somewhat on the Cybersecurity one. Also I am planning on taking the 2 American History CLEPS soon and so I'm going through those lectures.

The main thing about them is that you can listen to them so its great for mutli-tasking or when doing something boring.