They are correct.
The market for full price, DRMed eBooks is miniscule.
If they are going to DRM an eBook, we want it to be at a throwaway price. If we don't like the book, are done with it, etc. we have to throw it away because the DRM prevents us from reselling the ebook (like we can do with a physical book).
That "throwaway" price is almost (if not) free. So there is no market for them.